I keep getting emails from people who have starter batteries installed instead of solar panels batteries. Some of them were substituted by solar installers or RV repair shops. Sometimes the emailer simply made their own decisions.

Stop it! Stop using engine start batteries for deep cycle RV battery applications. If a deep cycle lead-acid battery is specified and you get a starter battery you have been ripped off. If you buy an engine start battery and try to use it as a deep cycle RV battery you will not get the performance you paid for and soon it will fail. I don’t care if it says “deep-cycle” on the label. Don’t trust the label!

Lead-acid engine start batteries are not the same thing as lead-acid deep cycle RV batteries. Lead-acid start batteries are less expensive, but they are designed to provide quick, high amperage draws and not designed to provide long-duration low current. Deeply draining engine start batteries will quickly kill them. Stop using engine start batteries — except to start your engine.

STARTER BATTERIES ARE FOR STARTING

Starter batteries provide a quick burst of power to start your engine. After that, they need to be recharged right after they are used. They only use a small amount of their potential energy to accomplish the engine start so recharge is quickly accomplished. Occasionally they will act as a buffer if the draw exceeds the alternator power. This also is a very short duration event. Your engine does not run on the starter battery, it runs on the alternator.

Modern lead-acid engine start batteries are especially bad selections to use as a deep cycle battery. A modern lead-acid engine start battery will be labeled as “low maintenance” or sometimes even “zero maintenance”. This means that you cannot add distilled water to the cells. Recharging the battery quickly will cause the fluid to release hydrogen gas. The gas is then vented — you need the liquid to be in liquid form (inside the battery) so that it can release the stored energy. If the liquid is gone — so is the battery.

Starter batteries are not designed for a long-term low amperage draw and will quickly die if used in this way. They are not designed for multiple deep discharge and charge cycles. Starter batteries will completely fail if drained to 50 percent of their full capacity only a few times. Modern lead-acid engine start batteries are very intolerant of deep discharge and will die in only a few months if used as a deep cycle battery.

COMBINATION BATTERIES

This is where the marketing department has deceived the consumer. Later I will explain the differences on the inside of the battery that makes one battery a lead-acid start battery and one battery a lead-acid deep cycle battery. You can have one or the other but not both.

There are no good combination lead-acid batteries that excel as both starter batteries and deep cycle batteries. Simply put, if the label doesn’t say AGM or Gel (and has a high price) and if the battery doesn’t have fill caps, it is nearly certain to be a lead-acid engine start battery.