Checking battery

Whitty said:
SmartGauge battery monitor. Super simple installation, highly accurate state of charge meter. Cannot run out of synchronisation with the batteries. Volts display, Charge Status (percentage), user programmable alarm functions, about £150 i have one its great.
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Good kit, I have one. But probably not an appropriate choice for the OP's boat, which sounds quite small and simple. To give an idea of "the health of the battery whenever I arrive at the boat", an eBay digital voltmeter for a couple of quid seems a reasonable fit.

Pete
 
prv said:
Good kit, I have one. But probably not an appropriate choice for the OP's boat, which sounds quite small and simple. To give an idea of "the health of the battery whenever I arrive at the boat", an eBay digital voltmeter for a couple of quid seems a reasonable fit.

Pete
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+1. Posh boats with big battery banks and big loads may justify £150, but I paid a couple of pounds for an ebay digital voltmeter that agrees with my digital multimeter to within a few 1/100ths of a volt. Arriving on the boat, I turn on the power and it gives me an immediate idea of the state of charge and, while the voltage drops when I start drawing power, for a given load, it drops consistently as I discharge the battery, so I can see at a glance roughly where I am.

It's a bit more complicated than this, but for practical purposes, for an ordinary lead-acid battery, a resting voltage of 12.7 is 100% 12.2v is 50% charge. It's time to turn stuff off as you'll start to damage the battery if you make a habit of going lower.

At 12.0v, the battery will probably be damaged. I ran both my batteries down to <3v once. Bad idea. The domestic battery went in the bin, but the starter one came back and lasted another couple of years. On my boat, under an average load the voltmeter shows a couple of tenths lower, so I pay attention at 12.2 and start turning non-essentials off at 12.0.

Wire the voltmeter from downstream of the battery isolator through a fuse of 1amp or less (the drawn current is a few milliamps, but you're protecting the wiring, so it wants to be as close to the switch as convenient) to a convenient place on the return to the negative battery terminal.
 
Highndry said:
Boat is fitted with basic equipment and battery rarely used apart from a NASA bidata and a small amount of manoeuvring on electric outboard off and possibly on moorings once, perhaps twice a week. There's a 10a solar panel fitted whenever she's sitting on the trailer or mooring. What I'm after is a way to tell, at a glance, the health of the battery whenever I arrive at the boat. Is that doable? Perhaps, even with a hand-held instrument?
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Use a cheap solar panel regulator (six quid from ebay, for example, at http://www.ebay.co.uk/itm/Solar-Cha...lator-Safe-10A-12V-24V-UK-STOCK-/261472382412) with red/amber/green battery condition lights. It's only a basic voltage indication but will be quite sufficient for your needs - no need to go messing about with expensive battery monitors. Your 10W (I presume, not 10A) solar panel will have a blocking diode in it somewhere which you need to remove or bypass to connect to the regulator.
 
A voltmeter used when not on charge or under load and after resting can give you a reasonable idea of the state of charge of a battery that is in good condition.
What it won't necessarily do is tell you whether the battery is in good condition or not.
You can have one that gives you an apparently good voltage but then when you put it on load you find it has very low capacity.
Proper battery monitors, though not perfect, can give you much more information.
 
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