Installing telecom batteries in the solar bank
These Varta UPS-216H and UPS-144H stationary batteries were used as starter batteries for emergency diesels situated at cell phone towers. They’re about ten years old, and were replaced due to old age, so I intercepted them on their way to the recycling facility.
They’d been sitting on float charge their entire lives, so they had considerable cell balance issues when I got them. However, due to their impressive build quality, most of them recovered very well, with specific gravities well within spec for all cells! They have reasonably high internal resistance for their size, but definitely not high enough for it to be a problem in my application.
Note that you should NEVER connect large batteries in parallel without a way to disconnect them reasonably quickly; my system requires the undoing of both terminal bolts in order for a battery to be taken out of circuit, and is EXTREMELY DANGEROUS. If a battery suffers enough damage to short out critically after outgassing, causing internal arcing, like in the case of a shorted cell, it could EXPLODE.
THERE IS A REAL EXPLOSION HAZARD TO THIS SYSTEM. COPY IT AT YOUR OWN PERIL. YOU HAVE BEEN WARNED.