Parallel batery strings 1

[1379power]

Are there any proven disadvantages of using parallel strings of VRLA batteries, when each string consists of batteries of different capacity? Of course the prefferred solution is to have all batteries identical however this is not allways practical when upgrading an existing system.
Thanx.

 

[electrageek]

1379power

I am not a battery expert but I have started up and installed quite a few battery systems. With a single string battery bank the charging voltage and current is controlled by the battery charger. For Lead Acid type batteries the charging volts per cell is very important and is carefully controlled by the float charge setting on the charger. Too high of a voltage on each cell causes overcharging and the evaporation of the electrolyte and too low causes a weak charge. Many times I have seen failed batteries removed, and not replaced, and the maintenance personnel forget to lower the charging voltage to commpensate and then the other batteries began to have problems. The maintenance free, or sealed, batteries still have the same requirement for charging voltage and can be damaged if they are not kept within tolerance. Your idea of parralleling different types of batteries seems that it could have a problem getting the correct charging voltage for the different battery cells.