Battery Cell – Electrolyte Level Increasing When Charging ??

[ThreeCW]

I have never seen or heard about this before … how about you?

It appears that the electrolyte level in the middle cell one of my cart batteries has been slowly increasing over a number of charge cycles. Coincidently (or not), the fluid level in the cell next to it (adjacent to “+” terminal) dropped to the top of the plates and needed to be topped off. The middle cell fluid level increased by perhaps an inch … about 1/3 into the sight well … it started at perhaps 3/8” above the plates. The third cell fluid level stayed about the same (adjacent to “-“ terminal).

Cart is a 1998 Cushman Hawk with 48 V battery pack with 8 pieces of 6 volt US Battery US 125 XC2 – 242 amp hour. Batteries are Feb. 2013 vintage. Two (2) of the 8 batteries had previously failed (shorted cells) and were replaced with rebuilt / blemished batteries of a similar rating. Battery charger is a Lester Summit Series Model 28000 – 48 V x 19.5 A. My typical charge pattern has been to charge after ½ to 1 hour of use with the pack at an 80 to 90% state of charge. I check water level frequently (every week or two) and usually end up adding de-ionized water off once per month. Battery caps are the Speed Cap type – twist the levers and remove all three at once. Battery cap rubbers are all in place with no leakage noted. I have not been washing the cart but occasionally wash off the top of the batteries with a jug of rain water. I am confident that no water has entered during washing.

Pack voltage after a fresh charge plus a few 150 yard trips to the barn is 51.6 V. Individual batteries are 6.53, 6.50, 6.43, 6.52, 6.42, 6.36, 6.45, 6.44 V. Perhaps not surprisingly, the battery with the problem is my 6th battery with the lowest voltage of 6.36 V.

I also checked SG of all cells … ranged from an SG of 1.240 to a high of 1.290 at 64 to 74 deg F electrolyte temperatures. Again, not surprisingly, the lowest SG cells were in battery 6 (with the increased electrolyte level) at SG 1.240 (“+”), 1.250 (middle) and 1.265 (“-“) at 69 deg F.

I ended up transferring the excess electrolyte from the full middle cell to the two outer cells of Battery 6. I suspect that Battery 6 is in some kind of failure mode and will have to be replaced soon. Perhaps this might help me expedite a switch to Lithium batteries.

Can anyone suggest what is going on here?

Regards, 3CW