Bill Schoenherr of Midland, Michigan, asks:
"My gelcell batteries are 8 years old and although they are showing no signs of age, I have abused them by discharging them below 50 percent of their capacity. I’m considering replacing them because we cruise the Great Lakes in the North Channel area and I would hate to have them fail up there. Are TPPL batteries (Odyssey) still the way to go? I can’t find any additional information on alternatives like the Oasis battery technology."
Nigel Calder replies:
You’ve done well with your gelcells, but before discarding them you might want to perform a capacity test. Bring them to a full charge and then discharge them at 1/20th of their rated capacity (i.e., 5 amps for every 100 amp-hours of battery capacity). You’ll need an ammeter to measure the discharge rate. If you don’t have one on board, there’s an excellent clamp-on DC ammeter that reads to 400 amps in the Sears on–line catalog for $60: part # 03482369000 (sears.com).
Use the boat’s interior lighting to impose the necessary load. You’ll need to monitor voltage and stop the test when it falls to 10.5 volts. If this occurs in less than 16 hours, the battery has less than 80 percent remaining capacity and should be replaced. If it holds up for 16 or more hours, you can hang onto it a bit longer. Be sure to recharge it immediately to avoid damage.
You’ll get maximum benefit from Odyssey TPPLs and other such batteries only if you have charging devices that are powerful enough to take advantage of their high charge-acceptance capacity, and if you spend time running the engine just to charge batteries. In this case I would seriously consider them. But you may run the risk of burning up your alternator, because the batteries will drive it to full continuous output for extended periods of time.