I have four 6V Lifeline deep-cycle sealed lead acid batteries which are now 9 years old and have failed. Not surprising, but it is the way they failed very suddenly that leaves me curious as to how this happened and if I did anything wrong with them over the years. Maybe some here with more experience has some possible explanation.
Basically, these batteries were bought new together, connected in series to provide 24VDC, were only used a handful of times per year, rarely allowed to fall below 50% discharge, stored in a fixed stationary location (not in a vehicle or boat), and kept on float charge with a temperature sensor the rest of the time. My understanding of battery aging and failure is that as batteries age, they lose capacity from charge cycles and sulfation. But based on what happened to me, there must be more to it than just that!
Recently, I called this 9 year old battery bank into service. About 10-15 minutes later, the battery at the positive (+) end of the series suddenly failed. At rest, that battery still reads 6.42V like when it was new. But now with just a small load, the voltage drops to 2V or so and almost no amps come out. Remove the load, and relatively quickly the battery voltage rises back up to 6.42V.
The other batteries in the bank seemed fine, so I decided to switch to a 12V battery bank configuration to use the remaining three batteries for however long they last. However, similar results occurred with the next 2 batteries: again after 10-15 minutes of service, each battery at the positive (+) end of the series failed in similar way! I’m left now with just one working 6V battery at the negative (-) end of the series, the same one that has been there all three times, but I have no facility to charge it or utilize just 6V. I’m also doubtful the battery would function under load any longer than the others, even if I had an application to for it.
So, I’m confused here about what might cause this kind of battery failure. It’s almost like a fuse blew inside the battery, or lead plates cracked, or cells shorted, upon applying the load. Does age alone eventually cause this? Strange too that it was always the battery at the positive end of the string, coincidence? What process must be going on inside the battery to cause this, and is there anything that I could have done differently over the battery life (like not keep them on float charge for years) to change the form of death?
Not planning to perform an autopsy, but would like to get an understanding of what could eventually go wrong in a lead acid battery to cause this type of age failure. Thanks for your thoughts.