Start Me Up

It’s been a perfect day. You find the ideal cove for your on-the-water party, and after dropping the hook, you crank up your new 1,000-watt stereo with a powered subwoofer. The blender’s working overtime, making all manner of frosty beverages for the crowd. After dark, the mood lighting comes on. But when it’s time to go, you hear the dreaded clicking sound from your engine’s starter. You didn’t take care of your electrical bidness. So how does a social butterfly host avoid the “paddle of shame”?

Pack Enough Battery Power

The first thing you have to figure out before you determine how many batteries you need and what size they need to be is simple: How much power does your boat consume? A good off-the-rack boat stereo system might have a 200-watt stereo with four 6.5-inch speakers. Your actual power usage depends on how loud you crank it. Van Halen fans will likely use more power than your average smooth jazzophile. The battery usage for a system like this isn’t too bad. An average group 27 deep-cycle battery holds about 90 amp hours (Ah), which should never be run down more than 50 percent. A 200-watt stereo only draws around 2 amps per hour, so most deep-cycle batteries should deliver more than 20 hours of run time without drawing it down too badly. (I’m using severe in-the-ballpark figures to keep it simple.) Find out the precise draw with a $15 multimeter that will show amps being used, among other measurements.

In general, gel and AGM batteries handle being discharged better than liquid lead/acid models, and your house and cranking battery should always be of the same type. The gold standard — for the wakeboarding types who usually have bigger stereos than a 1980s disco — are Optima Blue Top batteries, which are expensive ($225 to $300) but really robust.

Subwoofer amps and high-end systems tend to be more power hungry. It’s not unusual to see one rated at 1,000 watts or more, so if you are “going for it,” you should err on the side of caution and add another deep-cycle battery wired in parallel to your existing deep-cycle one to keep it a 12v system. Wiring it in series makes it a 24v system, which can fry your electronics. If you’ve installed new stereo components or accessories and want to know if your battery supply will support it, try it out for the length of time you would run it, and do it within paddling distance of home before you go all the way across the lake.


Most boats with two or more batteries have a battery switch that has a 1, 2, or BOTH setting. The only problem with the older-style switches is there are only three terminals on the back, so the battery wires share one of the poles and are not properly isolated. To make matters worse, many people set the switch to BOTH and take the risk of running both batteries down or exposing electronics to voltage dips and spikes when cranking the engine, which is not good for electronics.

The better way to manage multiple batteries is with Blue Sea Systems’ Add-A-Battery. It has four terminals in the back, meaning you can wire your engine (and items such as bilge pumps) to one side and all your electronics to the other side — no shared wires. So when you turn the switch on, the starting battery connects to the engine and the house battery connects to the electronics. But if the engine is running and separated from the house battery, how can that battery be charged by the engine’s alternator? The solution is an Automatic Charge Relay, which comes with the kit. When the engine is running and the voltage rises, a relay closes and joins the house battery to the engine’s circuit to charge it. But when the engine is off, the relay opens and isolates the starting battery, thus preserving its full charge when you are using components on your house battery and depleting its charge. It also has an emergency “combined” setting that allows you to join the batteries together to start the engine if the starting battery has somehow weakened. The beauty of this system is that everything is automatic; you just turn it on and off, without having to figure anything out. The system is available at West Marine for $143.

Backup Plan

Battery packs are great insurance to make sure you don’t spend the night on the water involuntarily. They used to be pretty expensive, but the price has dropped significantly. You can get a Cen-Tech Power Pack with a jump starter for only $40 from Harbor Freight. You can use it to charge cellphones, run 12v accessories and jumpstart your boat if needed, which is a great way to keep the draw down on your boat’s batteries. A more expensive, but more powerful higher-tech product, is the Weego Jump Starter, which runs from $99 to $179.