Whilst sitting around doing nothing, per my doctors order (ok, as little as possible), I find myself perusing the RV and boat forums. There are several VERY recurring themes, some of which are comical, some not so much. The one about a battery being depleted and/or going “dead” for no “obvious” reason is a tiny bit fascinating to me.
I do not understand why electrical systems are so poorly understood. I suspect it is simply because many people have no experience. However; if operating an RV and/or boat that requires battery power, every owner should get educated.
The bulk of the dead battery reports go something like one of these:
- RV/Boat in storage for x months, battery now dead.
- When I last used my RV (last summer) the battery worked fine, now something is wrong.
- My battery show 9.6 volts, why is it not working?
- My ratty old battery charger has been charging my battery for the last six months and now battery is dead.
- My battery seem to be out of water. Is this bad for them?
Everyone using a typical lead-acid or AGM battery, read this carefully:
- Batteries do not last forever.
- Batteries do not hold a charge forever.
- Discharging a battery below about 50% capacity will do some amount of damage (each time).
- A 12 volt battery voltage level has nothing to do with its state of charge. In other words, a 12 volt battery is not 50% discharged at 6 volts (it is dead/unusable when gets to that point).
- All vehicles have parasitic loads and will eventually deplete a battery unless it is completely disconnected. It does not matter if you use the “battery disconnect” switch.
- A “smart” charger is a 3 or 4 stage charger that senses the state of the battery and provides only what is required. A fully charged battery is maintained at “float” voltage (around 13.5 volts) which avoids “cooking” the battery.
- Unless it is a “maintenance free” or AGM battery, it requires maintenance in the form of distilled water.
Please note; I am talking about the fairly standard 6 and 12 volt DC lead-acid and AGM used in cars, RV’s, boats, general aviation airplanes, etc. If you have a high-tech LiPo battery bank (or other), this article may not apply.
So there, no reason for anyone to have another battery problem again! 🙂