Can I drop in lithium batteries?

Dear Boat Doctor,

I’d like to change my house batteries to lithium. The capacity and efficiency of charging is really compelling, but I don’t want to have to replace my alternator and shoreside charger. Is there a drop-in replacement that would work?

Dave Ross

Superior, Wisconsin

Dear Dave,

Lithium battery systems are amazing, but these are not simple systems; they require some planning and infrastructure. I can give you a few tips, but I urge you to consult with an expert for a full system design.

I assume you are referring to lithium iron phosphate battery technology, often referred to as LiFePO4 batteries. I would not recommend any other lithium battery technology.

A stock internally regulated alternator will not stand up to the rigors of charging lithium batteries. The charge acceptance rate of the batteries is too high for the alternator, and will charge for too long a time, to the point where the alternator will overheat.

Regulation in this configuration is typically done with a lithium-capable DC-DC charger. You will connect your alternator to your start bank and configure a DC-DC charger to charge the lithium house bank. The trick is configuring the DC-DC charger to charge at a rate the alternator can continuously deliver without overheating. For most alternators, this is roughly 40% of their rated peak current. 

Your shoreside charge will need to charge with a lithium charging profile. These new batteries work differently than lead acid batteries, and the wrong charging protocol will shorten their life.

There are no true drop-in lithium batteries. You must take a system view to realize the full benefit of this new technology.

Why doesn’t the vang hold up the boom?

Dear Boat Doctor,

My Selden vang doesn’t hold up my boom. I removed the vang from the boom and I can compress it by hand. What’s going on here and is there a fix?                                                              

Shirley Voight

Fort Lauderdale, Florida

Dear Shirley,

This is a very common problem with Selden rigid vangs. The vang has a gas cylinder in it, similar to the cylinders used to hold open the trunk of your car. Over time, the cylinder will lose its oil seal and will go weak. Fortunately, replacing the gas cylinder is very easy.

The first step is getting a new cylinder; Selden calls these a “Rodkicker gas spring.” You can get a spring from any Selden dealer, and there are many online. To replace the cylinder, simply pull the two parts of the vang apart, slide out the failed cylinder, move the old end fittings to the new cylinder, and slide the new part in. It should be a 20-minute job at most. The new cylinder will come with instructions for your review.