There's no problem recharging them with solar panels, and they sell a bunch of them for that purpose. However, as opposed to their batteries, the panels are overpriced and you can do better elsewhere.

How big a battery you need is important, but so is your charging system. And intended use.

Charge some batteries wrong and you will destroy them. A good example is an AGM battery, charge it fast with a high current you will boil the fluid and separate the jell from the fiberglass mat inside.

Use an auto starting battery in place of a deep cycle battery and it gets deep cycled a few times and you will destroy a battery.


There is a lot of things to take into account to get an off grid system to work right. It not as simple as just going to the store and buying a battery and then having a charger for it.

Yup. Auto batteries are for cold cranking, namely, generating a lot of current for a short amount of time, e.g., 30 seconds, and then they need to be immediately recharged.

Deep cycle batteries are for extended usage between charges, and you can bring them down to 20% of capacity without damaging them. (Try that with a car battery.) You can get enormous capacities for deep cycle batteries for use on boats, RVs, solar powered homes, etc.

Sealed lead acid (SLA) batteries are very nice, as you can run them down, they hold their charge fairly well when not in use, you can trickle charge them so they're always ready to go, and they generally don't explode or leak.

There are lots of types of batteries and they all have unique performance characteristics, such as how long they hold a charge, number of recharge cycles, whether you can trickle charge them without damage (you can't do this to the Lion batteries), how fast you can safely charge them, whether they can be reconditioned, usable temperature ranges, etc., etc. Far more info to write about batteries than would fit here!

Companies like PowerPort will give you lots of information about how best to recharge their products.

The 12volt Side of Life

http://www.ccis.com/home/mnemeth/12volt/12volt.htm

How about just picking up a portable jumpstarter?

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=40615

It's portable, 24Ah, already comes self contained with the necessary outlets, and no need to mess around with complicated charging systems, just charge it from your car cigarette lighter. Plus it comes with cables so you can jumpstart your car if your main battery dies. I have one wired up to one of my vehicles right now, so it's always topped off when the car is running. I was going to go the dual battery route also, but I did this in the meantime and it works well enough that I might just keep it like this.

I think a solar system would be more trouble than it's worth. Even if you were to get one large enough to put out decent power, it wouldn't be portable anymore, and the smaller ones aren't always capable of recharging SLA batteries. A car alternator can recharge the battery in a fraction of the time that it would take the solar panel. Carry an extra 1 gallon gas tank and you have enough fuel to recharge your batteries for a really long time.

Edit: I see that swampdonkey already brought up the idea.

The problem with these portable jump starters is that they are notoriously unreliable. They usually are at least a year old (battery wise, The battery has been doing nothing for a year, not good) before they get on the store shelves, the jell cell batteries in them don’t like to be overcharged, the things generally don’t have a great charge controller in them so when you plug it in and leave it the battery gets too much voltage and the battery while showing a full charge doesn’t last very long.

I worked for a guy that owned a used car lot and had a lot of these things laying around that were not that old. It’s less expensive to just buy another jump box then it is to replace the battery in it.

If you are going to have a portable reserve battery, you should invest in a good adjustable charge controller and figure out the voltage charge limits for the type of battery you are using. Most people think this is not needed and just plug the battery into any available power source and call it good.


Portable battery power is about more then a battery, it’s a reserve system. The battery is only one part of that system. The charge controller is just about as important as the battery if you want it to work for a long time.

+ 1.

The car battery chargers that work through a DC lighter socket take forever, and you'll do much better off with the portable units that jump the battery directly. Then let the alternator do the charging as God intended...

Also, batteries start to go bad once they leave the factory. That's why car and deep cycle batteries are dated and you shouldn't buy one older than 6 months. Even then, they are frequently on the way out. I bought a car battery with a CCA (cold crank amperage) of 800 at CostCo. Took it straight to one of those car care places that tested it at 500. Went straight back to CostCo. Either it was bad from the start, improperly stored, or they changed the date label. Take your pick.

Edit: Oh, you were talking about a portable jump starter -- my mistake. They've actually saved me a couple of times. Buy one with a built in trickle charger; leave it plugged in. If you're going on a long trip, throw it in the car. Replace the battery (if possible) or the unit every few years. I wouldn't go off the beaten path without one.

I read someplace that all battery makers (Every one of them) lie about the amperage rating of the batteries they make. The best you can hope to get out of even the newest battery is 75% to 80% of its amp ratings.

As far as the trickle charge for the jump boxes if it doesn’t have a good controller to cut off the charge (and they don’t) it will overcharge the batteries. When a battery is fully charged, the charge needs to be turned off, even a small charge is too much.

It is possible some fly-by-night battery retailers exaggerate the batteries true capacity. But there aren't very many battery manufacturers and all the big ones are on average pretty straight-up in their ratings. Verging on quite conservative for the premium producers. Generally, as long as you go with a reputable battery producer you will get what you pay for. Often more than their stats say.

Some of the confusion is that people think batteries are like buckets, you get out what you put in. You never do. Even if you could you really wouldn't want to. Once the voltage on the battery drops your ability to get the energy out in a usable form comes to an end. The battery still had energy remaining but not enough to do anything with.

Also, before the voltage drops below usable levels the battery is getting worn down. The lower you take the battery the fewer cycles you can get out of it. The rule of thumb is that only a third of the batteries capacity is usable if you want to get the maximum life out of the batteries. All the reputable battery manufacturers are quoting the accurate figures on what the batteries will do. it is up to you effectively use what you buy.

One of the best manuals for setting up a system comes from the world of boating. Most libraries can hook you up with a copy of:

"Boatowner's Mechanical and Electrical manual" by Nigel Calder.

he has an in-depth discussion of various systems, batteries, chargers, and how to put them together to do what you want.

Yeah, I'd have to agree. Just about any auto supply store will give you a fairly detailed printout of a battery's characteristics for free. After returning my CostCo bargain, I bought a different cold crank 750A battery that tested slightly above specs.