Groups U1 and U1R Batteries - Dimensions, Features, and Recommendations

BCI Groups U1 and U1R batteries are general purpose batteries often used in medical and security applications, in wheelchairs, electric scooters, golf carts, lawnmowers, and other garden tools, camping, etc.

BCI group U1 and U1R batteries are mostly AGM and Gel-Cell batteries with wet/flooded batteries being phased out. Also, lithium-ion U1 batteries are appearing on the market, offering higher capacity, a larger number of charging/discharging cycles, and lower weight, but they also cost more, at least initially.

Updated: March 29, 2021.

Groups U1 and U1R batteries physical dimensions are (L x W x H) 7 3/4 x 5 3/16 x 7 5/16 inches (~197 x 132 x 186 mm) with the U1 battery having a positive terminal on the left side, and U1R having a positive terminal post on the right side of the battery (hence the 'R' as part of the label).

Note: terminal posts vary too, so when ordering, be sure to order the battery with proper orientation and with proper terminal posts (for example, F7, F3, B2, etc.).

The following chart lists the most popular BCI Group U1 batteries and their most important features and specifications:

As one can see, most U1/U1R batteries are intended for general purpose use, although some are designed as starting-only batteries.

Also, some models (for example, VMAXTANKS V35-857) are labeled as deep-cycle batteries by their manufacturers, but in fact, they are true high-performance dual-purpose batteries.

Anyway, BCI Group U1 batteries on average feature ~35 Ah 20h capacity, they are mostly Sealed Lead-Acid (SLA) Absorbent Glass Mat (AGM) non-spillable, vibration-resistant batteries.

High-performance/starting U1 batteries feature 300-320 CCA Amps, while general-purpose U1 batteries are able to provide at least 300-350 Amps for 5-10 seconds - these batteries are commonly used as starting batteries in lawn tractors, power generators, and other similar applications.

Manufacturers rarely state actual Reserve Capacity (RC - number of minutes that a new, fully charged battery can provide 25 Amps at 77°F/25°C while keeping the voltage above 10.5 volts) value, but they often provide constant power and constant current discharging tables, helping the users predict discharge characteristics for different applications.

On average, a good U1 battery is able to provide 19-20 Amps for ~60 minutes. However, a very popular high-performance VMAXTANKS V35-857 battery is able to provide 25 Amps for 75 minutes - which is significantly above the average.

SLA U1 batteries on average weigh 23-26 pounds (~10.4 - 11.8 kg) and thanks to often built-in carrying handle, can be easily carried around by an adult person.

Lithium-ion U1 batteries are not as common as AGM/Gel-Cell U1 batteries, but they offer huge weight savings, increased number of charging/discharging cycles, larger capacity, and similar.

For example, VMAXTANKS VPG12C-50Li is a lithium-ion U1 battery with built-in protective electronics (Battery Management System - BMS) that protects the battery from overcharge, over-discharge, short-circuit, and similar undesirable conditions.

Also, it features a nominal capacity of 50 Ah (vs ~35 Ah AGM 20h capacity), it weighs just 12 pounds (~5.4 kg) and can be discharged with 50 Amps continuously with almost no drop in capacity.

Additional features of VMAXTANKS VPG12C-50Li include battery On/Off switch, LCD display, and USB charging ports (5V/1A, 5V/2.1A), allowing the unit to act as a small power station.

But, VMAXTANKS VPG12C-50Li should not be used for starting/cranking applications - it is able to provide 150 Amps for 3 seconds or 100 Amps for 5 seconds, but no more. Also, VMAXTANKS VPG12C-50Li operates at a slightly higher voltage (up to 16.8 volts) and should be charged with smart battery charters intended for lithium batteries (or at least with lithium-ion battery charging mode).

VMAXTANKS VPG12C-50Li is commonly offered with a smart battery charger that can charge these types of batteries safely, prolonging both runtime and operating life.

Note: every lithium-ion battery has different features of their built-in BMS (Battery Management Systems) and they should be used as recommended by their manufacturer. For example, VMAXTANKS VPG12C-50Li should NOT be connected in series for obtaining higher voltages (24V, 36V, etc.), but can be connected in parallel for obtaining higher capacities.

In the end, all these features dictate the price:

As starting batteries for smaller internal combustion engines, Weize LFP1235, Power-Sonic PS-12350, and Mighty Max ML35-12 batteries are able to provide 330-350 Amps for at least 5 seconds, which is usually more than long enough for such engines.

Note: if the engine doesn't start after a few short attempts, let the battery 'rest' for a minute or two.

As deep discharge batteries, ExpertPower EXP12330 and Weize LFP1235 are able to provide at least 20 Amps for 60 minutes without the voltage dropping below 10.5 volts.

Note: VMAXTANKS V35-857 is a clear deep discharge winner when compared with other U1 batteries (25 Amps, 75 minutes, down to 10.5 volts), but it also features a 300 CCA value (300 Amps for 30 seconds, with the voltage NOT dropping below 7.2V, at 0°F (-18°C)).

On the other hand, Power-Sonic PS-12350 is able to provide 25 Amps for 60 minutes, but with the voltage drop down to 9 volts (1.5 volts per cell) - such deep discharge can significantly decrease the number of charging/discharging cycles and should be avoided.

Group U1 Batteries in 24 Volts Systems

Group U1 batteries are commonly used in 24 volts systems - two batteries are connected in series, doubling the voltage.

When connecting AGM/Gel-Cell batteries in series, be sure to get the very same batteries - same battery model, from the same brand, preferably from the same batch.

Many established brands offer their U1 batteries in pairs for 24V systems or as a bundle of 3 batteries for 36V systems.

For example, when two U1 batteries are used to power a wheelchair with 2x250 watts motors at 24 volts, one may expect a maximum current load of 20.8 Amps (~21 Amps) @24V. Several U1 AGM batteries are able to provide such current for at least 60 minutes.

Since wheelchairs are not used at full power, actual operating time can be several times longer.

Group U1 Batteries as Kayak Trolling Motor Batteries

Group U1 batteries are often used for powering small 12V trolling motors used on kayaks, pontoons, and other smaller crafts.

Kayak trolling motors feature a maximum current of 20-30 Amps, with 25 Amps being their "average maximum" current.

U1 batteries are able to provide 25 Amps for slightly less than 60 minutes - around 45 minutes, having few more minutes as a safety margin.

But, lithium VMAXTANKS VPG12C-50Li while weighing half the average AGM battery, can provide 25 Amps for almost two hours (at least double the time of the average AGM U1 battery).

VMAXTANKS V35-857 is not the cheapest AGM U1 battery on the market, but it is well-liked by people appreciating its starting features (300 CCA), but also its 75 minutes RC value.

ExpertPower EXP12350 is able to crank smaller internal combustion engines, but it is often used as a cheaper deep cycle alternative of VMAXTANKS V35-857.

Weize LFP1235 is a very balanced design and is one of the most popular batteries in this class.

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Long Story Short: Group U1/U1R batteries are general-purpose batteries, intended for backup, automotive, solar, marine, and other applications.

When choosing the right model, be sure to pick the battery (or batteries) according to your own needs and requirements.