The question is often asked: Can I use a 12V 4Ah battery instead of a 12v 5Ah battery? The reverse question is also asked. The answer may not be earthshattering but will provide perspective and peace of mind. As you prepare to buy a replacement 4ah or 5ah sealed lead acid battery pause here and learn the differences and similarities in this edition of What’s What in the Battery World. Specifically we will use Universal Power Groups UB1240-F1 and UB1250-F2 SLA batteries as our reference point. The battle of the 12V 4Ah vs the 12V 5Ah begins now.

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Specification5Ah Battery4Ah Battery
Part No.ComparedUB1250-F2UB1240-F1
Dimensions - Inches13.54 x 2.76 x 4.0013.54 x 2.76 x 4.00
Voltage12 Volts12 Volts
Capacity AH5Ah4Ah
Approx. Weight Lbs3.05 Lbs2.95Lbs
Battery TypeFactory Sealed AGMFactory Sealed AGM
PolarityLeft PositiveLeft Positive
Warranty12 Mo.12 Mo.
Terminal TypeF1 or F2F1 or F2
Retail Cost$18.95$15.95

F1 vs F2 Terminals

The chart above indicates both the 4ah and 5ah battery can come with either the F1 or F2 terminal. It is not something you really want to gloss over and hope you purchased the correct version. You may end up discovering your home security alarm battery connectors are too small and will not attach to your battery. Or worse yet your connectors are a little big and fit loosely on the battery terminals. If not addressed, this could allow slippage and generate a spark causing a short and perhaps a fire.

These F1 and F2 terminals can be found not only on the 12V 4Ah and 12V 5ah batteries but on most all the smaller 6 volt and 12 volt lead acid batteries from 22ah down to 0.2Ah. The F1 terminal sometimes referred to as T1 terminals will be 0.187 inches (3/16”) wide. The UB1240 pictured above has the F1 terminals. The F2 or T2 terminal is 0.250 inches (1/4”) wide. The UB1250 pictured above has the F2 terminals. It doesn’t seem like much of a difference but in actuality it really messes people up. Luckily, if you ever find yourself in the position of staring at the wrong terminal set on your SLA battery, it can be remedied quite simply.

For the vast majority of applications you can attach an F1 to F2 or F2 to F1 converter. These tiny adapters cost way less than it would take to ship back and exchange your incorrectly purchased battery. They easily slide onto your existing battery terminal to adjust the width to the desired 3/16” or 1/4” size. The length of your terminal will end up about a half inch longer.

A wise friend shared with me once that he purchased a set of terminal adaptors and taped them to his alarm system battery. That way he never had to worry about remembering which terminal type he needed. When the time came to buy a new replacement he would either tape the adapters onto the new battery or slide them on the terminals and use them.

Can the 4Ah and 5Ah Battery be Used Interchangeably?

Looking at the chart above, we can clearly see that these two batteries are the exact same physical size and share the same voltage. The only difference is in the amp hour capacity verified by the slight weight difference. Now most people choose to upgrade their 12V 4ah battery to the 5ah version. But if you wanted to save a little cash, or the 4ah was all that was available you could replace a 12V 5Ah battery with the 4 amp hour one.

This is what the exchange would look like when presented in a linear percentage metric:

Going from the 4Ah to the 5Ah would mean your application could run up to 25% longer.Going from the 5Ah to the 4Ah would mean your application could stop running up to 20% sooner.

So you need to ask yourself, will this difference in run time truly affect the ultimate outcome of how you are using the battery? There are many situations in which it will have no effect as the battery is simply their as a backup source of power should the primary power source have a hiccup. If the power actually went out, 4ah or 5ah might mean the difference of a couple of minutes and is really insignificant. In an application where you are constantly draining the power down over 7 or 8 hours and need to extend this another hour or two then upgrading is essential.

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There are literally thousands of applications for these little 5Ah and 4Ah batteries. It would be impossible to list every specific application and give a recommendation. The best we can do is highlight the broad categories such as home security alarms, UPS backup systems, home medical devices, and two wheeled electric scooters.