By far the most common problem with lead acid batteries is losing charge over time. It might not sound like a problem if the battery becomes discharged – after all you just recharge it again right? Unfortunately this isn’t the case, and the key to owning a battery that lasts is making sure its charge doesn’t drop too low, whilst at the same time making sure you don’t over charge it.
Your boat’s electrical system is of course absolutely critical, so any electrical issues you face can put you out of action, which is of course extremely frustrating.
A major weak link in the electrical infrastructure of a boat is the battery/batteries. Boats are typically fitted with lead acid batteries because they are the tried and tested method of providing the 12 volts needed by the various systems on board. In this day and age we all know that lithium ion batteries are lighter, and less problematic, however the uptake for their use on 12 volt systems is probably still a way off yet. Why? You’re probably looking at 10 times the cost to fit lithium batteries at present, so for now at least, lead acid batteries are here to stay.
Unfortunately cost is about the only benefit that lead acid batteries do have, and as a diligent boat owner you need to stay on top of maintaining them so that they don’t cause you problems when you can least afford them.
The Problem With Allowing a Battery to Become Fully Discharged
Most boat electrical systems allow for battery charging directly via the engine or engine alternators, whether that’s the house batteries or starter battery. Typically you have a switch which enables you to switch between the two, or indeed charge both at the same time.
Careful planning and battery monitoring ensures you shouldn’t get into a situation where your house batteries in particular have drained to a damagingly low level, but let’s suppose you do make this mistake, what are the implications?
Allowing batteries to discharge completely actually causes irreparable damage, such that you won’t be able to charge them fully the next time you try. Make the same mistake again and you’ll find the problem gets worse until such time that the battery becomes completely useless and buying a new one is the only solution. With a decent set of marine grade batteries this can easily run into thousands of dollars, so it’s an expensive mistake to make.
The Problem With Overcharging Batteries
If you thought that the remedy for allowing batteries to discharge too much is simply to overcharge them to compensate, think again.
Whilst batteries don’t take on a lot of additional charge when they are ‘full’ they do still draw a trickle of additional charge, which can in time damage the battery permanently.
Whilst the effect of this process is likely to be more noticeable in boat/leisure batteries you might have experienced it on a smaller scale when overcharging devices such as your phone or tablet. If you’ve ever grown frustrated that your phone seems to discharge more quickly than when you first bought it, it might not just be your imagination, rather it could be this very effect in action.
Keeping Batteries Alive and Kicking for as Long as Possible
So it’s pretty clear batteries are quite fussy things in terms of the amount of charge they do and don’t like to hold, suggesting that the key to their longevity is maintaining their charge within acceptable limits, neither too much charge not too little.
Bear in mind however that all batteries have a shelf life, and will change their chemical composition to the point of being useless eventually, it’s simply your job to try and prolong their shelf life for as long as you possibly can.
In practical terms this means keeping your batteries topped up (but not overcharged) as close to permanently as you possibly can. During the summer season when you’re out on the water frequently this is a far easier task as you’ll have eyes on the electrical system and be running the engines frequently. Off season is of course a different story.
The general rule of thumb is that batteries permanently lose 10% of their charge for every month of inactivity, therefore if you possibly can you’ll want to recharge your batteries once per month in the off season. After all your boat might be out of action between October and March, which could in theory see your battery capacity diminish by 60%!
The good news is that house batteries on board boats tend to be what’s known as ‘deep cycle’ batteries, meaning they are designed to take a lot of discharging to borderline detrimentally low levels followed by recharging, with this cycle repeated many times over. In other words, they can take a fair amount of abuse! Nonetheless you should still adopt all the best practices described above to ensure they last as long as they possibly can.
Ideally you’ll want to store your batteries off your boat and in the warm to prevent the other major problem that winter brings; freezing temperatures. Depending on where you live and the state of the battery this won’t be an issue, with battery acid (electrolyte) in a healthy battery not freezing until temperatures get well below zero. However it’s a different story if the battery is discharged as the electrolyte solution can be heavily composed of water and less of sulphuric acid, meaning the electrolyte will freeze at 0°C (32°F). When this happens it’s game over for the battery.
It’s worth having a bit of discussion about a specific type of lead acid battery known as an AGM or ‘Absorbent Glass Mat’ battery. In simple terms the battery acid in an AGM battery is suspended within and absorbed by glass matting, rather than just being a liquid solution. This means the battery cannot be spilled, which is pretty useful on a boat where there can be a fair amount of movement in all directions.
Although considerably more expensive than traditional lead acid batteries, AGM batteries have a number of other distinct advantages that you might be interested in.
- Approximately 30% lighter than traditional flooded batteries- again on board a boat where weight is directly related to performance, this can only be a good thing
- No risk of freezing
- Retains charge for far longer and can sit in storage for far longer without requiring a top up recharge. So you can be fairly confident about leaving AGM batteries untouched during winter (as long as you leave them in their charged state), and being sure they will be fully functional by the time you get back out on the water in spring
Removing and Replacing the Batteries From Your Boat
If you do decide to remove your batteries for winter you’re going to want to make sure you do so properly to avoid any damage to the battery, or yourself!
Depending on how well your boat has been designed you’ll find the batteries aren’t always easy to get to, so accessing them can be a chore in itself. Once you’ve located them however follow this checklist:
- Open up the battery box. This may require loosening some ratchet straps or other mechanical catches. Once you’ve got eyes on the battery or batteries the first thing to do is a visual inspection for acid leaks around the terminals. If you see any gunk or whitish deposits resembling salt, then do your best to clean it off with a wire brush. To try and prevent future corrosion it’s advisable to apply an anti corrosion grease to both the terminals and ends of the battery connector cables as this helps prevent corrosion, especially in the harsh conditions of a marine environment
- Remove the negative (black) connector cable first. You’ll likely need a pair of spanners or a spanner and a socket wrench, and depending on how corroded things are, a fair amount of elbow grease!
- Repeat the process with the positive (red) terminal, but take great care not to allow connection between the two battery terminals to take place (ie. completing the circuit), if you do there will be a blinding flash and things might begin to melt! Not good!
- Carefully remove the battery and place it safely to one side.
- If you haven’t already cleaned the metal connectors on the end of the battery cables now is a good time to do so, again use the wire brush to clean away any debris.
- Position the new battery in the correct place in the battery box or compartment and reattach the terminal connectors, connecting the positive terminal first and negative second. Ensure the connecting bolts are tightened.
- Replace the lid or retaining straps
How to Charge a Battery Out of The Boat
If you’re using traditional ‘flooded’ lead acid batteries and wish to remove them from your boat and keep them topped up throughout the winter, clearly you won’t be able to use your boat’s engine or generator to charge them. Instead the best option is to use an automotive trickle charger.
When selecting and using said trickle charger it’s important to make sure it has a setting that ensures it doesn’t deliver at anything more than a trickle, otherwise too much charge might be delivered too quickly, ultimately leading to overcharging and damage to the battery. Bear in mind you’ll only ever be charging 10 to 20 percent of the total charge of the battery at a time, so it won’t take long to get fully charged up, even with a trickle charger.
You may have heard that storing batteries directly on the floor leads to them discharging over time, or they might even damage the floor should they leak. Modern batteries don’t really suffer from this problem, and various technological innovations have largely rendered the need for such precautions unnecessary. Obviously if the battery is visibly leaking you’ll know you’ve got problems, but otherwise placing batteries on the floor is not an issue.