Sega Nomad Internal Battery Mod v2.0 (now with 3000mAh cells)

In this post, I’ve documented the upgrade of my previous 2300mAh internal battery mod to 3000mAh cells. This post is not a complete “start to finish” guide, it’s only meant to cover the steps taken to fit the larger cells. Refer to my previous post for the original guide and supplement from this post as necessary.

This post is written for informational purposes only. I assume no liability for damage done to your equipment or for any injuries you may incur attempting to emulate this project. Please be careful when working with electricity and vintage electronics.


Battery Test Time-Lapse


I found the new cells by accident while shopping for parts for another project. I had used two 2300mAh cells (86x56x3mm each) originally, but these new 3000mAh cells (90x60x3.5mm) are only slightly thicker, and should just barely fit length- and width-wise.

Some additional plastic will need to be removed from the shell first. That extra 1mm of combined thickness sounds like peanuts, but just as before, squeezing these cells in is a game of millimeters.

It may not look like it, but the new cells are 31% larger by volume (probably the largest that can physically fit), but offer a 30% higher capacity.

For anyone wondering about the numbers printed on the cells, these are the cells’ dimensions. The new 3000mAh cells are 3.5mm thick, 60mm wide, and 90mm long, so they’re labelled with “356090”.


Table of Contents


Bill of Materials

Not including tools & misc parts I already owned

  • 2x . . . 3000mAh 3.7V LiPo cells [ link ]
  • 1x . . . 1.6mm Red LED (15-pack) [ link ]
  • 1x . . . 1.6mm Green LED (15-pack) [ link ]
  • 2x . . . JST Connector Plug Cables (10-pack) [ link ] (optional – see the “Connecting The New Cells” section)


Shell Modifications

To accommodate the larger cells, more of the internal plastic needs to be removed in multiple locations. Aside from just fitting the cells, I’m also trying to keep at least a tiny gap between the top cell and the processor above to help minimize heat transfer.

The “existing conditions” from the previous mod – the blue circles are where cuts were made in the previous version of this mod.

First up is the piece I’ve dubbed the “battery terminal block”. The external battery pack used to clip on here; the Nomad’s original battery terminals would stick through the two rectangular holes to make contact with the pack. This piece protrudes into the Nomad farther than anything else, but due to its shape it can’t be fully trimmed down without leaving a gaping hole in the shell (which is obviously a problem aesthetically). I used my Dremel drill to very slowly and very carefully grind down the top of it as much as I could. In the end, I gained close to 1mm of height.

Next, the wedge I originally cut from the D-pad support post needs to be widened. To measure the new cut, I sat a small piece of cardboard on top of the “battery terminal block”, the lowest point the cells would sit, and marked a line on the D-pad post. Then I measured up about 8mm (the combined thickness of the new cells, plus a little extra), and ground out as close to these marks as I could.

After that, a few spots around the perimeter needed some work. The new cells are longer and wider than the previous (which really pushes the limits of the available space), so they’ll now overlap with the two small “ridges” along the bottom of the shell, and below the cartridge slot. The stump of the security screw post needs a trim as well.

For these cuts, I used the same method as the D-pad post – I sat a piece of cardboard on top of the “battery terminal block” and used it as a guide to trim it to the same height.

With that done, one of the screw posts for the 2nd-player controller port needed to be trimmed. One of the stabilizing fins on the side is in the way of the cells’ protection boards. I used my Dremel to grind down the side, but I accidentally slipped and cut into it a little… whoops! It’s unfortunate, but since there are two posts for the controller port, I’m not worried about it.

The blue outlines are cuts from the previous version of this mod, the red outlines are the new cuts I’ve made.

With the shell done, there’s one more piece that needs to be trimmed: the controller port itself. The face of the port extends outward on both sides for two screw holes, though neither are actually used. The side with the letters “UNION” printed on it needs to be trimmed to fit around the cells (the red dashed line).

Using masking tape and paper towels, I made a smock to protect the rest of the board from dust and debris while I ground down the side of the port.

Replacing the Nomad’s circuit board, it now fits perfectly. The cartridge connector sits flat against the shell without having to put any pressure on it.


The New LEDs

The final obstruction is the 3mm “charging status” LED connected to the charging board, which extends up far enough to press against the new cells. I tried sanding down the side of the LED to flatten it, but I couldn’t get it low enough to not hold up the cells (without breaking it, anyway), so the solution was smaller LEDs. Unfortunately I couldn’t find bicolored LEDs smaller than the previous 3mm, so I’ve settled on using two separate 1.6mm LEDs, one per color. The package shape of these particular LEDs allows them to lie pointing downward, so the flat backing will be flush with the top of the screw hole they’ll sit in.

The old 3mm bicolor LED vs the two new single color 1.6mm LEDs.

The wiring is simple; the original bicolor LED had 3 terminals, two cathodes (the negative terminal, one per color) and a shared (common) anode (the positive terminal). The new LEDs can be wired in the same configuration, where each anode connects to the same wire.

The complication with using these LEDs is an aesthetic one – their terminal legs are clearly visible through the screw hole. To cover the hole, I got creative and rigged a lens using a plastic bottle cap and hot glue.

I traced the hole onto a piece of cardboard and used it as a guide to cut a bottle cap to fit. It took a few tries, but once I had one that fit snugly, I used a thin layer of hot glue to hold it in the hole, then laid the LEDs on top of the glue and covered them with a small piece of electrical tape to hold insulate them.

I’m not… thrilled with the results, but it’s decent enough (if anyone has a better idea, I’m open to suggestions!). It does help to diffuse the red charging LED a bit (which is very bright), but the green LED is surprisingly dim – not the lens’s fault, but still disappointing.


Connecting The New Cells

Optional – I decided to make a small addition to the battery’s wiring. In the event I needed to disconnect the cells again, I added some JST connectors inline between the cells and charging board. I found a pack of pre-wired connectors with 4” wires on eBay, so I took two pairs and trimmed the wires down. After desoldering the old cells, I soldered half of each connector pair in their places. The matching side of each connector was then soldered to a new cell, and heat shrink was used to protect the solder points.

I didn’t realize I’d wired each cell with a different gendered connector until it was already soldered and heat shrunk, but it works just as well.

After this, everything fit right back into place in the shell; the charging board kept its original spot and the new cells took the spot of the old. I tucked the connectors along the edge of the shell near the kill switch and replaced the circuit board (there really is just so much wasted space in this system…).



Similar to the previous version of this mod, I need to test the battery life and temperature. The previous 2300mAh cells clocked in at 3hrs31min, so scaling from that, the new 3000mAh cells should last around 4hrs35min. Unfortunately there’s a complication with this estimate; in the time since this first test, I’ve also replaced and rewired the LCD as part of this separate project (which I’ll post in a few weeks), exploring a more power-efficient method of wiring the LCD. I haven’t tested its effectiveness yet either, so we’ll just have to see what happens.

Using the same digital thermometer as the previous version, I charged the battery to full, let the system cool to room temperature, then filmed the Nomad, a stopwatch, and the thermometer and let it run until the battery ran out.

In the time test, it blew past my 4½hour estimate, stopping at 5hr12min, which I mostly attribute to the LCD wiring. What I can’t quite account for is why the system ran cooler than it did with the 2300mAh cells. The Nomad had been sitting in the room for a few hours before before starting the test, so I’m sure the room temperature (i.e. starting temperature) was practically the same as the last test. Maybe I ended up with better clearance between the cells and processor this time? I wouldn’t think so, but either way I’m happy with the results.



There’s not much more to say than last time. I’m thrilled to have over 5 hours with this new setup, and it’s even running a little cooler than before. It’s also worth noting that even though the system itself may be a little heavier now, it’s still lighter when comparing it to the cumulative weight of an unmodded system with a tumorous battery pack hanging off the back.


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