Old and New Batteries Together

It is generally considered bad practice and inefficient because the string is only as good as the worst battery.
A better idea is to replace them all but keep the best of the old ones. As this process repeats you will accumulate a stock of 'old but useable batteries' these can then be strung together an used.

Del

As Del says don't mix old and new, it's false economy

Hi, as said it's bad practice, since if used in series the old one (low amp) will be over heating since high power will pass through it for high load and the voltage will also drop causing high current, thus all batteries willbe overheating /overload.

But in parallel this will not affect the load/ batteries. As a result voltage will be same at all bat pottential.

In any case don't mix old/new batteries togerther, as explosion may accour in severe case of high load.

My batteries are only 10months old (100AH, Rocket make, 12V SMF). They are 26nos. for my20KVA UPS. Now i am upgrading the UPS to 30KVA which needs 30Batteries.

If i can not buy the complete new set of 30Batteries, what should be the line of action i should follow.

Please can you give more details about the electrical connection of the 26 existing batteries, so that an alternative solution may be propose.

In general all same battery capacity may be connected in series and not same capacity in parallel.

So if you can't afford to buy 30 new batteries, then the new one need to be in parralel with the old set. Never mix old and new in series as it will be overheat/load.