Battery Backup System

This can work up to a point; you can increase the "run time" of the UPS on battery, but you will not increase the power output of the UPS, IE; if it's a 500W output, that's not going to change. The gain would be a longer backup period. Charge/Recharge time will be longer, and the software that controls the UPS will probably not reflect the larger battery capacity. A final note, you will most certainly void your warranty with such modifications :)

Tom D.

For discharge your idea is probably good, but with "smart" systems there is some risk in making this assumption.

For charging your idea is a bit tougher. The bigger battery will put a larger demand on the charging circuits. A current limited charger MIGHT still be happy but take longer to charge. But, there is the RISK that the charger might not be able to supply the current demand of the battery. Also, a "smart charger" might get confused and thus it might make you unhappy. Equipment damage, FIRE, etc. are all on the list of things that might happen when power systems are modified without knowing what you are doing.

Overall, the answer is it might work but I suggest "NO" unless you know for sure.

GA for saving me the time to write exactly the same thing.

If you got desperate you could try increasing the size of the battery one or two sizes but you MUST keep the same battery chemistry and number of batteries as the charging circuit won't work properly with lead acid car batteries, and there is a chance it won't work potentially causing damage to your UPS and certainly voiding the warranty in any case.

In conclusion, you get what you pay for and the small cheap UPS's have very little expansion capability (built to the lowest cost after all). If you want a longer run time you will need to purchase a larger UPS.

I would say if you have to ask you proberly shouldnt touch it.

the biggest problem as somone else has said is the recharging of the bigger battery

why not get a say 500 watt inverter or whatever your thing is drawing connect it to a battery and charger and leave the charger runniung all the time then when mains power fails the thing will keep running ie basicly a cheaper UPS

Should I mention that not all lead acid batteries and battery packs operate on twelve volts like a car battery. On second thought, I'd just start another long winded argument that spanned more than one thread if I did that.

It's a no... doing that will destroy your charger, all battery back-up systems have their own chargers that are proportional with the battery that comes with it. You can try replacing the charger, if it's a separate module, or, redesign the charging system circuit using higher current components.