Trailer Battery Charger: AC-to-DC, DC-to-DC, and Solar Dump and Travel Trailer Battery Chargers

Regardless of the trailer type, trailer batteries are often hardworking batteries that often operate in anything but ideal conditions.

As such, these batteries have to be charged and kept fully charged when the trailer is not in use. The most common trailer battery chargers include AC-to-DC, DC-to-DC, and solar battery chargers and their combinations, allowing the trailer users to have their batteries charged regardless of the situation.

Published: January 3, 2023.

Intro to Dump and Travel Trailer Batteries

Dump and tilt trailer batteries provide power for the lifting mechanism, which is usually hydraulic.

Thus, dump trailer batteries must be very tolerant to mechanical impacts, vibrations, low and high temperatures, must accept charge well, must be very reliable, and operate regardless of the remaining battery charge. Also, if there is any glitch in the electric system or sudden need for extra power, they must be able to provide it, even if only for a few seconds.

Travel trailer batteries also must be very tough, but they are rarely subjected to mechanical and electrical wear and tear like dump trailer batteries.

They also must be able to operate properly in low and high temperatures, but again, travel trailers provide better means of protecting and insulating the batteries than dump trailers.

The obvious choice for trailer batteries are large lead-acid and lithium batteries, with both types having their own pros and cons, including:

• Lithium batteries are lighter, can tolerate a large number of charging/discharging cycles, and can be recharged faster,
• Lithium batteries have built-in Battery Management Systems (BMS) which protect the batteries from unwanted events, like overcharging, over-discharging, low and high temperatures, short circuits, and similar,
• Lithium batteries are spill-proof, no maintenance batteries that can operate in any position,
• Lithium batteries require dedicated lithium battery chargers, perform badly in low conditions, and high temperatures can simply cause BMS to shut off the battery,
• while wet/flooded lead acid batteries are not maintenance-free batteries, AGM and Gel-Cell lead-acid batteries are maintenance-free batteries,
• lead-acid batteries should not be discharged below 80%, preferably below 50% in order to prolong their operating life,
• lead-acid batteries don't feature BMS, so they can easily provide huge currents if required for whatever reason,
• lead-acid batteries are much safer batteries that can be easily connected in series or parallel.

Thus, generally, one should consider the following:

• Dump trailers: lead-acid AGM battery or battery pack. These batteries are tough, durable, and very reliable, even if there are occasional electric glitches and extra power requirements. The main reason for not considering lithium batteries are their internal BMSs, which protect the batteries from any extra load - it would be very unprofessional to have the load partly lifted, and the batteries turned off by their BMSs because of some extra event in the middle of the job.

On the other hand, if maximum continuous current and maximum surge current of lithium batteries fit your needs, consider lithium batteries as well. Just be sure to connect lithium batteries in parallel or series as their manufacturer recommends and to charge them with dedicated lithium battery chargers.

• Travel trailers: lithium battery or battery pack. These batteries are lightweight, they accept charge faster, they tolerate a large number of charging/discharging cycles, and can be discharged down to 100% DoD while still supporting thousands of cycles.

AGM Battery Example: Odyssey Battery ODX-AGM31A (31-PC2150) Extreme Series AGM Battery

Odyssey Battery ODX-AGM31A (31-PC2150) is a dual-purpose BCI Group 31 Battery featuring a nominal voltage of 12V, nominal capacity of 100 Ah, CCA of 1150 Amps, MCA of 1370 Amps, HCA of 1545 Amps and PHCA (Pulse Hot Cranking Amps) of 2150 Amps.

The battery is offered in several sub-models, generally with different battery terminals and left/right battery terminal orientations.

It tolerates up to 400 cycles down to 80% DoD, which is a very good result for lead-acid batteries.

Also, it operates from -40°F (-40°C) to 176°F (+80°C) and can be recharged in 4-6 hours completely.

Of course, in order to prolong its operating lifetime, charge and discharge the battery at room temperature as often as possible and don't discharge the battery below 50% DoD.

Odyssey Battery ODX-AGM31A (31-PC2150) is far from being a cheap and lightweight battery (it weighs 77.8 lbs, 35.3 kg), but what You pay is what You get.

Note: There are many other suitable AGM batteries that can be used as trailer batteries, especially if You are looking for budget-friendly models, but for hard-working batteries, one should not go cheap ...

For more reviews and recommendations, feel free to check the Odyssey Battery ODX-AGM31A (31-PC2150) AGM Battery Amazon link (the link opens in the new window).

Lithium Battery Example: Li Time (Ampere Time) 12V 100Ah LiFePO₄ Deep Cycle Battery

Li Time (former Ampere Time) 12V 100Ah Lithium Iron Phosphate (LiFePO₄₎ battery weighs only 24.25 lbs (~11 kg) which is more than 3x less than the Odyssey ODX-AGM31A battery.

The battery comes with a built-in Battery Management System (BMS), which monitors the battery condition and protects it from unwanted events.

Also, the BMS allows the user to connect up to 4 batteries in series and up to 4 batteries in parallel (4S4P max.), creating rather large battery packs.

Note: always connect lithium batteries in parallel and/or series only as their manufacturers recommend.

Also, the Li Time 12V 100Ah battery tolerates a much larger number of charging/discharging cycles:

• 4000 cycles down to 100% DOD,
• 6000 cycles down to 80% DOD,
• 15000(!) cycles down to 60% DOD.

(No, we didn't add one zero too much to the number of supported charging/discharging cycles.)

However, Li Time 12V 100Ah LiFePO4 battery is able to provide "only" 100 Amps (~1200W) continuously and 280 Amps (~3300W) for 5 seconds, after which BMS shuts off the battery unless the current drops below 100 Amps.

On the other hand, a new, fully charged Odyssey ODX-AGM31A (31-PC2150) battery can provide ~3170 watts for 10 minutes!

So, if You are looking for a battery or battery pack that is lightweight and cycles well, but there is no need to power extra large loads, go for lithium batteries.

But, if You are satisfied with 300-600 cycles down to 50-80% DoD if You can tolerate a somewhat heavier battery, but You want a battery that will do its job even in the hardest conditions, go for a high-quality AGM battery.

For more reviews and recommendations, feel free to check the Li Time 12V 100Ah Lithium Iron Phosphate Battery Amazon link (the link opens in the new window).

How To Charge Trailer Batteries

The easiest way to charge the trailer batteries is using the truck's trailer outlet and default wiring, right?

Well, not exactly. The problem is that the charging wire and charging current found in, for example, a 7-way trailer outlet is strong enough to maintain the trailer's batteries charged and perhaps to charge them very slowly.

That also means that if You have, for example:

• several jobs with your dump trailer throughout the day that the battery will be discharged sooner or later, and You will have to stop somewhere and somehow charge the battery, which is not good for your business.
• to change the location of your travel trailer, your trailer battery (or battery pack) will not be charged while on the road. When You come to your new location, instead of enjoying your time, You will have to find other means of charging the trailer battery.

This can be remedied using so-called DC-to-DC battery chargers with some extra wiring and new electric connections.

Trailer DC-to-DC Battery Chargers

DC-to-DC battery chargers are connected to the truck's 12V (or 24V, depending on the truck) electric system and are used to "isolate" the trailer battery from the truck's alternator, charging controller, and starting battery.

Additionally, a good DC-to-DC battery charger should also:

• support charging of different battery chemistries, including lead-acid (AGM, Gel, Flooded) and Lithium Iron Phosphate,
• include protection for the starting battery in the form of a D+ ignition cable - when the engine is not turned On, the battery charger is not charging the trailer's battery,
• isolates input and output to prevent voltage transmissions and potential errors and interferences,
• support the use of battery temperature sensor for accurate charging regardless of the season.

However, for the DC-to-DC chargers to work properly and not overload the truck's alternator and charge controller (voltage stabilizer), the minimal alternator power should be:

• Alternator <160 Amps: 20 Amps max. DC-to-DC battery charger,
• Alternator 160-180 Amps: 40 Amps max. DC-to-DC battery charger,
• Alternator >180 Amps (preferably 200+ Amps): 60 Amps DC-to-DC battery charger.

Note: check the documentation of your truck regarding adding a new battery charger just to be sure.

Also, the connecting wires must be thick enough to decrease energy losses.

Many brands offer models that do their job well. For example, Renogy manufactures DC-to-DC battery chargers supporting charging currents of 20A, 40A, and 60A.

Renogy 12V 40A DC-to-DC On-Board Battery Charger is one of the most popular models in its class for several reasons:

• supports charging both AGM, Gel, and Flooded lead-acid and lithium batteries,
• isolates input and output,
• includes over-voltage, over-temperature, and reverse polarity protection,
• supports the use of the D+ ignition cable and the LC current limit cable (40A -> 20A),
• supports the use of temperature sensor, etc.

Note: D+ ignition cable, LC current limit cable, and temperature sensor are NOT included by default.

The use of DC-to-DC onboard battery chargers is relatively simple, and they enable the truck to recharge the trailer battery whenever the truck's engine is On.

For example:

• if You have a pair of Odyssey ODX-AGM31A batteries connected in parallel (12V 200Ah battery pack) and they are discharged down to 50% DoD, Renogy 12V 40A DC-to-DC charger will recharge them from 50% DoD (50% SoC) to 20% DoD (80% SoC) in 90-120 minutes.
• if You have a pair of Li Time 12V 100Ah batteries connected in parallel (12V 200Ah battery pack), and they are discharged down to 80% DoD, Renogy 12V 60A DC-to-DC charger will recharge them from 80% DoD (20% SoC) to 20% DoD (80% SoC) in 2-2.5 hours.

Not bad for rather affordable units.

For more reviews and recommendations, feel free to follow the Renogy 12V 40A DC-to-DC On-Board Battery Charger Amazon link (the link opens in the new window).

Trailer Solar Battery Charger

Solar battery chargers consist of solar panels and a battery charge controller, which is connected to the trailer's battery.

Good solar battery charge controllers are mostly MPPT devices with high energy efficiency or budget-friendly PWM charge controllers with somewhat lower energy efficiency.

Solar panels can be portable or placed in the (semi)permanent position on the trailer, with each option having its own pros and cons.

Dump trailer and travel trailer solar battery chargers differ - solar panels are rather sensitive to mechanical impacts and vibrations, which is often hard to avoid in dump trailers.

Thus:

• Dump trailer solar battery chargers are typically used to maintain the battery fully charged while the dump trailer is not in use, with the battery being fully charged by other means, for example, DC-to-DC or AC-to-DC battery chargers.

Solar battery maintainers feature small solar panels, with the output power ranging from 5 to 20 Watts, rarely more - when connected to the battery, they keep it fully recharged over a longer period. However, if You can mount several larger solar panels and protect them from mechanical impacts and vibrations, there is no reason why not to charge the dump trailer battery with solar panels and a solar battery charger.

• Travel trailer solar battery chargers can be used as battery maintainers (smaller solar panels with charge controllers) and as battery chargers using several large solar panels connected to the MPPT/PWM battery charge controller.

Travel trailer solar panels range in power from 100W to 400W, but there are trailers with 800W or even more solar panels.

For example:

• On a good sunny day, 400W solar panels can operate with an efficiency of 60% for 10 hours, collecting 2400Wh of energy.
• An MPPT charge controller with 90% energy efficiency can send ~2160Wh of energy in the battery pack.
• A good lithium battery features charging/recharging energy efficiency in the 75-85% range, sometimes slightly more, depending on the battery condition, charging/discharging current, and similar.
• Thus, a lithium battery that has received 2160Wh of energy can deliver anywhere from 1620 and 1944Wh of energy.

Of course, these are general values, and the exact values can be found only by real-life testing.

Personally, for a dump truck, go for a solar battery maintainer, and for travel trailers, consider solar battery chargers since they can come in handy in many situations, especially when they are mounted permanently on the roof of the trailer using low-profile solar panels.

Trailer AC-to-DC Battery Chargers

Trailer AC-to-DC battery chargers are "standard" battery chargers that are plugged into AC outlets.

Good AC-to-DC battery chargers are microprocessor-controlled battery chargers that support charging of various battery chemistries, feature various safety features including temperature sensors, can be used as both chargers and maintainers, etc.

Most travel trailers come with an outlet allowing the users to connect the AC power to the trailer, automatically activating the onboard battery charger, which charges the battery as soon as AC power is available.

However, if the onboard battery charger is not present for whatever reason, it is possible to use standard battery chargers or to mount a new, off-the-shelf onboard battery charger.

Trailer AC-to-DC battery chargers differ in size from 10-20 Amps chargers for 12V 100Ah lead-acid batteries to 100+ Amps chargers for large lithium battery packs.

One of the very popular AC battery chargers is the NOCO Genius PRO50 battery charger, with a maximum charging current of 50 Amps (6V and 12V) and 25 Amps (24V), with an option to limit the charging current to 10 Amps.

Also, the NOCO Genius PRO50 battery charger supports the charging of various lead-acid batteries and lithium batteries, includes a full range of safety features, offers several advanced charging modes (Force mode, for example), etc.

Obviously, chargers like this one are not cheap, but neither are the batteries this model is designed to charge. And if this model is overkill, consider the NOCO Genius PRO25 battery charger.

For more reviews and recommendations, feel free to check the NOCO Genius PRO50 Battery Charger and NOCO Genius PRO50 Battery Charger Amazon links (the links open in the new windows).

One of the good things about AC-to-DC battery chargers is that they can be connected to power generators and used to recharge the trailer battery even when being off-the-grid, and the trailer doesn't feature an onboard battery charger.

Few Final Words

Trailer battery or batteries can be recharged in numerous ways, just be sure to find out which one (or more of them) fits your needs and preferences.

Also, these batteries and chargers provide strong currents, and any mistake, for example, in wiring, can cause fire, injuries, or worse.

So, whatever You do, it is your own responsibility.

If You are unsure how to recharge your trailer battery, we hope this article answers at least some of your questions.