Note: The article written here is directed towards emergency power systems in commercial facilites. This article is not directed towards home standby generators.
A lead-acid battery is just a box of electrons. The electrons are pumped out like water out of a bucket. So, the more you have in the bucket the more you can get out. For emergency generators you want the biggest battery you can get that will still fit in the battery tray.
Measure the battery tray. Batteries come in standard sizes like group 24, group 27, group 31, 4D, 8D, and 3EE. Your generator will use a standard size. The battery dealer should be able to recognize any standard size or find one close to the measurements of your battery tray.
Most cranking batteries are now rated in CCA, cold cranking amps. Buy the highest CCA rating you can get at the lowest temperature rating. Example: 1050 CCA @ 0? means the battery will deliver 1050 Amps @ 0?.
Watch the temperature rating! You want the lowest temperature rating you can get. Since a battery is a chemical reaction, and all chemical reactions become more active at higher temperatures, they can get a higher Amp rating by testing at higher temperatures.
• 1050 CCA @ 32 is good.
• 1050 CCA @ 0 is better.
• 1050 CCA @ 80 is a rip off!!!
Float voltage is the voltage you want your charger to maintain on your battery. We have found 12.75 to 13 volts DC is best. It won’t damage the battery, you will seldom have to add water, and it will keep the battery charged. (The float charge for a 24 volt systems should be adjusted to 25.5 to 26 volts)
Many battery dealers as well as generator manufactures recommend higher charge voltages. Don’t fall for it. This will result in higher battery failure rates.
The higher the Amp rating at 0? the better. Don’t worry that it might damage the starter by providing more Amps than are called for. It doesn’t work that way. With Amps more is always better.
Sealed batteries (maintenance free) are OK but batteries that allow you to add water are better. They are all the same inside, no matter what the battery guy says. Cranking batteries should be flooded cells, which means a minimum electrolyte level must be maintained. If you can’t open the cell to add water the battery is doomed.
“Maintenance Free” batteries are not maintenance free, just maintenance inhibited.
Deep cycle batteries are good, but they are not designed for cranking. The problem revolves around the busing that connects the plates within the cells.
Cranking batteries are designed to deliver high current for a short period of time, as is needed when cranking over an engine. Therefore, the buswork between the plates and connecting the cells together is built heavy to carry the high current. Deep cycle batteries, on the other hand, are designed to deliver low current for a long period of time, as with a trolling motor. The buswork that connects the plates and cells together is much lighter and may be damaged under heavy cranking loads.
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