Having good reliable power while camping in an RV makes the whole trip a lot more enjoyable. From reading lights for the evening news, to cappuccino makers for the following morning, having electricity makes camping a lot less like roughing it, and a lot more like staying at an outdoor hotel.

Trailer batteries, however, only have so much power, and don’t last forever. To keep them powered up and to keep the party going, Airstream owner Jonathan Schloo developed the CarGenerator, a portable power solution that will charge RV batteries without the hassles, mess, and smell of a traditional gas generator. Since all cars come from the factory with 75% of what you need to generate off-grid power, CarGenerator just adds the missing pieces; a pure sine-wave inverter, a weather-proof housing, and heat-proof, high-current booster cables. Voila; power.

All this work around trailer batteries has given Jonathan a deep well of trailer battery knowledge. At the Airstream Alumapalooza show in June, one of CarGenerator’s customers wondered if their old batteries were still holding a charge. In this video, Jonathan shows you how to find out, using a simple test, and an inexpensive tool from the hardware store.

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In a nutshell, if your battery depletes too fast, or charges too fast, it has probably lost much of its charge capacity. When it was new, your battery could take close to 100% of the charge for which it was designed and rated. As it ages, however, this capacity gradually decreases. If an old battery is only left with 25% of its original capacity, it will run down, and charge up much faster, since the “amount” of charge it can hold is much less. If you want power when you’re camping, it might be time for a replacement battery.