E-Maxx 3906 LiPo Battery Upgrade

My good friend Joe has an old E-Maxx – not wanting to miss out on any bashing and crashing fun, I had him dig it out. It’s an oldie but a goodie. A 1st Generation E-Maxx with dual motors, dual batteries and a 2-speed transmission. It’s the one with the chassis that looks like this:

It’s also a bit of a relic. NiMH batteries, brushed motors, and AM radio aren’t exactly state-of-the-art. But I don’t want to upgrade everything, I just wanted to get it back on the road – so where do we start?

Batteries

I know the old NiMH batteries were going to suck and what really impressed me when I came back to RC was how awesome Lithium batteries were. But do we need to get everything that goes along with it – like the newer EVX-2 electronic speed control that has low voltage cut-off? Heck no, we’re just trying to get it running. A simple low voltage alarm will do just fine.

So we’re going to get only batteries, but the 3906 chassis is sort of particular about fitment. Each battery sits (snugly) in a tray, and there’s battery strap that goes directly across the center of the battery. I found these 2S lipos that have the power and balance leads coming off of opposite corners, so they can sit in the tray nicely and have the strap close them in without crimping any wires.

But when it came time to put them in, we needed to trim one more piece. The old NiMH battery packs have rounded edges, where LiPos are square and about 2mm taller. The edges of the battery were getting hung up on part of the gear cover. The solution was to remove the gear cover and cut off the wire routing slots using a side-cutter:

Re-install the gear cover and the batteries will now snap into place. They’ll be snug, but they’ll fit. You’ll need to loosen the metal battery clip screw & post a couple turns to accommodate the LiPos thicker profile. Then you can use the original battery strap to hold everything in.

Here they are installed. The low voltage alarm is just zip-tied to the rear shock tower:

That’s it! Now go have fun 😎

I will warn you that the 1st Generation 3906 E-Maxx is capable of doing a backflip with some backwards/forwards throttle – but the old drivetrain is not up to the task. Next time we’ll tackle CVD upgrades to the newer E-Maxx units for better durability.