Due to the amount of traffic on the Boat Batteries page and the number of e-mails on the subject, I've decided to post some of the questions and answers here. I hope you find this information helpful! Have a question? You can e-mail me or post a question on our Facebook page!
About Your Boat Batteries in General:
R. Karl recommends the Dual Pro 15 Amp/Bank Professional Series 2 Bank Charger
Question from Frank about Battery Chargers:
I was reading your article and I have a question
about the battery chargers. When you say to get a charger that is
rated about 15% of the battery's amp hour rating. Where do you find
that on the specs of the battery. I have found as follows on the
deep cycle SRM-29:
So if you have a 125 Ah battery, you would generally be looking for a charger that can deliver 15% of that or approx. 20 amps. Then, as a rule of thumb, take the Amp-hour rating of the battery and divide by the charger rating (amps), and then add about 10% for the extra time to totally top off the battery, This will give you the approximate total charge time. In your case, your battery should take about 7 hours to charge using a 20-amp charger… but there are many other factors to consider when charging your battery: How much charge is left? What is the condition/age of the battery? What kind of charger do you have? Etc, etc and etc…
Just remember that a battery can, by self-discharging,
lose about 4% - 5% of its charge per week. So in one month’s time just
sitting in a warm garage, a fully-charged battery that started at 125
Ah may now have maybe 105 Ah available. Not charging it at all over
a four-month period can have disastrous effects! A good charger is even
more important than a good battery. And, as has always been the case…
you get what you pay for. I recommend a multi-stage charger with auto
shut-off. And check the voltage regularly. Never let a battery drop
below 80% of its rated voltage. For a 12-volt battery (which, fully
charged, should register about 12.7 volts), that’s about 10 volts.
Hi Jane –
One of those is called “internal battery discharge”. Parked in storage with temperatures like you described will quickly weaken your batteries, even if they are brand new and fully charged when the boat is parked. Opening up the battery box compartment may help some, but not much at those temps. Something called sulphation is always trying to occur; this is a process whereby sulphur molecules in the sulphuric acid electrolyte solution begin to coat the lead plates in your battery. It’s very much like plaque building up in your arteries. The coating continues to thicken until the battery eventually fails. Sulphation occurs mostly in batteries whose electrolyte level is low, leaving the lead plates exposed. So it obviously is important to make sure that electrolyte level in the batteries is topped off (use only distilled water) so that the plates are covered. But it can also occur – and more rapidly so – in deep-cycle batteries that are not fully charged as soon as possible after use; every minute you delay contributes to sulphation. And if they only get recharged to, say, 80%... then that leave a 20% opening for sulphation. This of course is exacerbated by the high temperatures in storage.
All that said – without electricity to keep the batteries charged between outings – the life of your batteries will definitely be shortened by a lack of proper care for them. As much of a pain as it might be to remove the batteries after each trip, leaving your batteries in the boat is definitely going to be detrimental for their survival. If your only option is to disconnect them, it would be better than to just switch them off, as there is always a tiny power drain when wires are connected. Then too, if you have no deep-cycle batteries, at least you will have less of a problem…
Bottom line: purchase the freshest batteries
you can find with the greatest amount of RC (reserve capacity) available.
And then look after them with the same great care you would any of your
other important pieces of fishing/boating equipment. As you are aware,
batteries are not an inexpensive item. Unfortunately, they seem to fail
at the time we least expect it and definitely when we don’t want them
to. Brand new, fresh batteries should have a useful life of about 48
months; it’s critical to ensure your batteries are always fully charged
and the electrolyte is topped off so that you get as much of that life
as possible from them.
Question from Annette about batteries
On to the Trolling motor… Of greatest
importance is choosing a charger that is designed for the type of battery
that it is intended to charge. The 6-amp charger that you purchased
may work just fine, but I don’t know any specifics about it, so I can’t
offer an opinion as to how well it will do the job. A good rule of thumb
is that the charger should provide a maximum of 20 amps for each 100
amp-hours of rating on the battery, and it should be able to fully charge
your batteries within 8 to 12 hours, max. It’s also worth considering
one that either shuts off or drops to a “float” condition when the battery
reached\s full charge. The extra money spent on proper batteries and
a good charger is well worth it in the long run, or you may find yourself
replacing batteries (an expensive proposition) on a fairly regular basis.
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