Installing an LSL AMP-L-START chassis-battery charger

Photo Credit: E. Don Smith

By E. Don Smith
December 13, 2016
Filed under Gear, Tech Tips, Uncategorized


Keeping the starting batteries topped off means your motorhome’s always ready to go.

If your motorhome is a modern unit built within the last decade, it may have come from the factory with a chassis-battery charger/maintainer. When plugged into 120-volt AC shorepower, this charger keeps your motorhome’s chassis (engine-starting) batteries topped off. Most of the factory-installed chassis-battery chargers are very small models that only deliver about 1 amp of current. While this may be enough to keep the starting batteries topped off in a perfect world, often you may need more current than they can deliver. Many motorhome systems such as slideouts, electric leveling jacks and engine starting rely on the chassis starting batteries, so keeping them properly charged is very important.

Nobody likes a dead battery, and with a few tools and a little time you can significantly upgrade the chassis-battery charger in your motorhome.

Nobody likes a dead battery, and with a few tools and a little time you can significantly upgrade the chassis-battery charger in your motorhome.

When your motorhome is in storage and connected to shorepower, most of us assume that the batteries are not being used and that the built-in 1-amp charger is enough to keep things topped off. However, unless you are using the main disconnect switches to cut off all parasitic drains, the batteries may still be under a small load. That small drain may be enough to prevent the batteries from being fully charged due to the low current that the typical chassis-battery charger provides. And, if your motorhome is a bit older, or is an entry-level model, it may not have a chassis-battery maintainer installed at all.

A good solution is one of the high-amp chargers on the market today that uses a different method of handling its charging duties. This type of charger connects to your house batteries and “steals” some power from them (when 120-volt AC power is available or a solar system is used to charge the house batteries) to provide up to 15 amps of charging current to the chassis batteries.


Remove all sources of external power by unplugging the motorhome from shorepower, disconnecting the solar panels (if any) and removing the negative battery cable from the house to the starting batteries, as well as the negative cable that connects the motorhome to the house batteries.


Locate the factory-installed battery charger and unplug it from the motorhome. On this motorhome, the charger was located quite a distance from the battery bank, so a long cable was routed through the electrical bay to the battery bank. We had to cut the cable to remove the charger since it was routed under the motorhome. We plan to repurpose the charger and use it at home for a car or lawn mower battery, etc.


After locating the wires from the charger to the motorhome, remove them from the chassis-battery terminals in the electrical bay.


Find a good location in the battery bay to mount the new charger. After drilling two pilot holes, we used sheet-metal screws to secure the charger to the panel.


The instructions from LSL detail several ways to connect the charger; we elected to connect ours to the same posts the original charger was connected to. Here we are measuring the proper length of 12-gauge wire.


Remove the insulation from each end of the wires, crimp on the supplied connectors and apply shrink tubing for a clean install. We repeated this for all three of the wires needed for the installation.


After crimping on the terminals, attach all three to the charger using the supplied lock washer. For safety reasons, be sure to make this connection to the charger before connecting the wires to the battery banks. If you connect the wires to the batteries first, the wires are hot and present a danger to you and the device.


Take the lead connected to the charger (labeled here Chassis +) and route it to the post where the original charger was connected. You can also connect it directly to the positive lead on the 12-volt chassis battery bank if that is easier. The installation manual provided with the charger describes other connection methods that you can use based on your setup.


For the ground wire, we used the negative terminal for the chassis-battery connection from the original charger. You can use any suitable ground, including a negative battery post.


Connect the charger to the house-battery bank. We used the positive post of the house battery that has the main cable attached to it coming from the motorhome. If you are in doubt about which of the many positive battery posts to use in the house-battery bank, test each one with a voltmeter and make sure the post you are connecting to reads 12 volts rather than 6 volts.


Although it is not a requirement, we used wire loom purchased from a local auto parts store to cover the wires and make them look similar to the OEM wiring.


Reinstall the negative battery cables to the house and chassis batteries.


After connecting everything properly you will see a light on the front panel indicating the type of charging that is occurring. If there is a problem with the house or starting batteries, or with the polarity of the wiring, there will be a red light indicating the problem area.


In addition to all the connectors needed for the install, the unit comes with a handy sticker that can be applied in the battery bay near the charger to clarify what the lights indicate.

Since your house batteries are usually the highest-capacity battery bank in the motorhome and are often charged by a sophisticated three-stage, built-in high-amp inverter/charging system, this makes them an ideal source to power this relatively new type of charger. Another advantage is that in most motorhomes both battery banks are stored in the same bay, making installation of this type of charger easy.

Two of the most popular chargers of this type are the Xantrex Echo Charger and the LSL Products AMP-L-START. For our purposes, we selected the AMP-L-START due to its lower price ($64.95 versus $129.99) and its widespread use in the motorhome market. LSL calls this a “diversion charger” because it steals a little of the charging energy from the house-battery bank and diverts it to the chassis batteries. This type of charger can be used in gas and diesel motorhomes and is designed to work on dual or single starting batteries; the house-battery bank can be of any size. LSL says the AMP-L-START can be used with all types of batteries, even if the house batteries and the chassis batteries are different types. In fact, the motorhome we used for the installation has mixed battery types, and the AMP-L-START has worked great for us.

Safety Tip


Since a battery cannot be turned off, be careful any time you are working with the positive battery terminal or any wires that are connected to the positive terminal. If you allow a hot wire to come into contact with metal surfaces or any electrical ground, sparks will fly.


In an area that potentially has battery gases present, this is something you need to avoid.

When the AMP-L-START senses voltages greater than 13.2 volts on the house batteries, it starts charging the chassis batteries. (The house batteries can be receiving voltage from solar panels, or the built-in inverter/charger.) This 13.2 volts is higher than resting voltage, and it serves as the trigger to activate the chassis-battery charger we installed. Once the house-battery voltage drops below this level, the charger goes off and does not add a parasitic load of its own to the battery bank.

This charger also has an overvoltage protection circuit that shuts it down during battery equalization, and it emits an audible alarm if the chassis-battery voltage drops below 11.9 volts. The device features an easy-to-see LED panel to advise you of its charging mode, as well as lights to indicate improper wiring.

Once connected, the AMP-L-START is a fully automatic system, and we have used it for several months with great results. According to the manufacturer, the AMP-L-START uses a tapered charge rate that is optimized to prevent electrolyte loss in the battery bank. Although it is a very easy charger to install, we have included a pictorial of the steps to remove your motorhome’s old charger (if equipped) and to install the new one. With only three wires to connect, the AMP-L-START is one of the easiest upgrades you will ever perform.


LSL Products
877-257-4655 (support only; no phone orders)


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