Why your batteries don't have the puff

You're not going to like this next bit. Because the chances are that if your boat's electrical system is having problems, the fault is not with the batteries it's probably in the original installation. That's not harsh judgment; it's a fact of life. Just think of it, water and electricity doesn't mix. Put the two together and there are bound to be problems - unless the system is absolutely perfect. Ergo, if you can't swear that your system is 100%, that's where you need to start looking.

Next, there's a massive difference with the way you use that electricity. At home of course, you don't really know it's there. But don't think that batteries afloat are like the battery in your car. For instance, when your car starts, that's it - a few seconds of heavy duty cranking to get the engine going and the battery has nothing else to do until you need to start again. All the car's electrical goodies: Ignitions, lights, air con, CD player are powered by the alternator.

OK, you have to start your boat too, so that's similar. But then what? You stop for the night, drop the hook and now all of the electrics run off the battery. Not just some of it, but all of it - lights, fridge, maybe heating, TV and whatever other appliances you might have installed. That's your whole life, running off a battery. And tomorrow night, the same thing. Which means the battery - or most likely batteries - have to be of the deep cycle type. They can take a long steady draw of its power, then charge up during the day to sustain you tomorrow night as well.

Which pretty well outlines all the health hazard areas you need to consider aboard your boat - the installation itself, the state and type of your batteries, and the ability to recharge them properly.

Your system

Here's one of those "don't try this at home" experiments to put the seriousness of installation - and that state in which your boat probably was when you bought it - in proper context. It's also to demonstrate why you can't afford to mess around with electricity, particularly in an environment surrounded by water. If your craft has a typical 100 amp/hour battery - and you were careless enough to drop a spanner so that it fell across both positive and negative contacts - boom - there's enough power there to melt the thing clean through. An ordinary 100 amp/hour battery!

So it makes kind of sense, does it not, to ensure that every single contact, every connection and every wire is properly sited and routed as carefully and clear of hazard as possible? You bet it does. Because every bad or crummy connection will sap your battery as much as any appliance - overloading your system and reducing your ability to recharge properly, there's no power when you need it.

Don't believe it? Sit a fully charged battery on what you think is a dry concrete floor and come back in seven days. Flat as a pancake. Why? Well, even the plastic casing that surrounds it is not a total isolator, so the battery can discharge straight through it.

And that's without even looking where the battery sits. Here we go, vibrated like crazy for hours on end by the engine and prop, condensation from above - a slight pooling of water, just the slightest, between terminals - and phoops, why doesn't the battery hold its power any more?

OK, you probably get the picture. Now go round and check, every cable and every wire splice. Is it clear and well away from bilge water? Is every join completely protected and free from moisture? Every NO you answer is another couple of amps heaped onto your system - no wonder the lights are dimming a bit, and the TV won't stay on past East Enders.

Your batteries

Now do the sums. Do your batteries have the grunt to do the job that's required of them? That means 'amperes' and we're not just talking load, we're talking your batteries' ability to bounce back after a night on the tiles - recharged and ready to face the same power load tomorrow night. Which means you have to allow for degradation from new, the fact that you can't recharge to more than about 80% without a very expensive 'smart recharger', and that to cope with surges you should have at least double the capacity your loading says you should.

Pessimistic? Sure - because every single appliance and kink in the wire has an influence on available power - and you're running on 12 volts DC, not mains. You want your stuff to work properly AND be able to recharge? Don't even guess, just multiply your loading by four that ought to do it - which means for a load of 100 ampere/hours, and work on 400 ampere/hours supply. And to make sure for real, don't skimp with El Cheapo batteries. Or the wrong ones.

Like, why won't an ordinary car battery work - they look the same don't they? If some bozo hands you this line, send him away with a flea in his ear. A car battery has to handle a very heavy load in very short snatches. For that reason its lead plates are very thin, to maximise their exposure to the surrounding sulphuric acid. Big power, very fast. The exact opposite of what you want, snugged up for the night with real ice in your drink.

That's why your marine battery is quite different. Thick plates instead of thin, to cope with steady, sustained load. And taller, with the top of the plates out of the electrolyte, so if the boat moves around in any kind of a seaway, none of that acid mix will slosh out. Is it dangerous? Only if you're careless and it's not in a properly contained, secure battery box that can contain leaks. Then it can burn your skin, eat through your clothes, make a hole in the hull, chuck out noxious gases and even explode in your face if your starter motor has a hard time kicking over your diesel.

Your charger

This is what brings your power system back to life. You can't afford to skimp on this either. So you should be aware that there are chargers, and there are chargers. One thing you don't want is a gismo that brute forces your batteries back without sussing the state they're in. Don't forget, your battery releases electricity by chemical action. When you're charging, it stores electricity by the same process. Overdo the rate and the chemistry runs amok, eating up the plates, overflowing out of the case and in worst cases, rolling over, dead. And at four hundred pounds a throw for some heavy duty marine batteries, that's not a game you want to play too often.

So it's worth spending a little extra on a charger that monitors your battery's state of charge, and backs off at about 80% to trickle the rest in - allowing the chemical reaction a chance to slow down to prevent your battery from cooking itself to death. A smart charger will also know that a battery cannot be returned to its absolute full state of charge. Though you might have had a mighty 12.7 or 12.8 volts to start with, that's where your brand-new battery will degrade from. As it feeds power, the acid eats up the plates, meaning there's no way it can ever be a hundred per cent again. True, but a good charger will do a good job.

Get a pro

Of course none of this is into the nitty-gritty of setting up your system yourself. With good reason. Take connections alone, that vital detail where actual wires make contact with the gadget they're supposed to supply power to. According to the Boat Safety Scheme (the standard by which your boat gets its inland waterways licence), the ends of every cable should either be crimped, swaged or soldered.

New to you? If you're not a crimper, swagger or solder, you need a pro to do the job for you. And that means a marine electrician, not a common or garden one - an agricultural electrician doesn't have that essential water on the brain. A proper marine 'sparks' does - and knows how to safeguard for it. No, he's not going to come cheap. But he is going to sort out the problems of being under-gunned every time you switch something on, chomping through battery after battery and getting nowhere. He's also going to make your system safe. No acid fumes creeping through the cabin while you're sleeping, no blow-back from charging too fast, power on tap when you need it - without that heart-sickening stall as your starter motor says "shan't, won't".