Long-Term KTM RC390: Lithium-Ion Battery Swap

Need to lose weight? A lithium-ion battery may be your best bet!

RC390 battery swap
With no lights or even a radiator fan, racebikes like the RC390 are great candidates for a lithium-ion battery swap.©Motorcyclist

In my last RC390 project bike installment (click here) I mentioned putting the little KTM on a diet. Besides attending to the fade-prone brakes (I'm working on that) all the RC needs at this point is refinement, and lightening a bike is one of the best ways to improve performance. And when it comes to cutting weight, replacing the stock lead-acid battery with a lightweight lithium-ion unit is low-hanging fruit indeed.

The RC390 is an especially good candidate for a li-ion battery. Here's why: While most sportbikes locate their batteries (and sometimes part of their gas tanks) under the seat to centralize mass and improve handling, the RC has its battery positioned directly behind the steering head, far from the bike's center of mass.

Bikemaster lithium-ion battery
BikeMaster’s li-ion battery is dwarfed by the RC’s stock lead-acid battery in terms of size, and in terms of weight it’s a scant 1.5 pounds. That’s a 4.9-pound weight savings.©Motorcyclist

And it's a big battery. To lighten things up I installed a lithium-ion battery from BikeMaster (bikemaster.com) that we had on the shelf in the shop. It's not a dimensional match (direct replacements are available), but the smaller DLFP-5ZS unit has ample power for this application. The RC is no longer running lights or even a radiator fan, so the battery just needs to dump enough current to turn the starter. At 1.5 pounds the lithium battery hacked almost 5 pounds off the RC, all for just $90. It doesn't get much easier than that. Actually, it does: Installing BikeMaster's smallest battery, the DLFP-4L-BS, would have saved another 4.8 ounces and costs $20 less.

Lithium-ion batteries are impressively light and powerful, but they’re not ideal for all applications since they’re delicate in terms of state of charge and can be finicky in colder weather. For streetbikes with accessories that draw on the battery when the key is off (alarm systems are a big culprit) a standard lead-acid battery is a better choice. But for sportbikes—and racebikes in particular—a lithium-ion battery is the quickest, easiest, and most affordable way to reduce weight.