Psion Revo Battery Replacement

A Psion Revo. Its two NiMH AAA cells are soldered in and sealed under the nameplate — which is why almost every surviving Revo needs this job.

Battery replacement for the Psion Revo and Psion Revo Plus (and the rebadged Diamond Mako).

The Revo was notorious for battery and charging problems. Unlike the 5mx, which takes two user-replaceable AA cells, the Revo runs from two built-in rechargeable NiMH AAA cells that are soldered to a connector and sealed inside the case. Twenty-five years on, essentially every Revo needs them replaced.

The job takes about half an hour with the right tools.

⚠️ Before you start

• Back up first. Following this procedure factory resets the machine.
• Read the whole procedure before starting. There is not a millimetre to spare inside a Revo, and it is an awkward machine to work on.
• Do not cut the battery wires — desolder them.
• Do not let the iron tip touch the cell body.
• Take care of the thermistor. It is wrapped in with the cells and the machine's charging depends on it.

What you need

Parts and tools

Item	Detail
Cells	Two NiMH AAA, nominally 700 mAh, with solder tags. Higher capacity works and gives longer running time, but see the charging note below.
Chemistry	NiMH only. Because of the way the charging circuit works, nothing else is recommended.
Tools	Scalpel or watchmaker's knife, small flat screwdriver, jeweller's screwdrivers, fine-tipped soldering iron
Consumables	Heatshrink or tape to re-encase the pack; hot-melt glue or silicone sealer — not superglue
Useful	Dental floss for lifting the nameplate without bending it

Ordinary shop AAA cells will not do: they must have solder tags, because the connector is soldered directly to them.

Disassembly

1. Prise off the Psion nameplate. Careful use of a scalpel avoids damaging it; a heftier tool or stronger glue will dent or deform it. Dental floss worked under the plate avoids bending the badge.
2. Under the nameplate are two pins sitting in retaining slots, holding the screen casing onto the silver case top. Prise each pin up and push it towards the centre to release the case top.
3. Lift the case top to expose the battery pack, the battery connector and the IrDA/power connector circuit board.
4. Unhook the left side of the battery bay to free it from the main body — this gives the clearance to lever the pack out. Be careful not to twist the ribbon on the right side.
5. Prise out the battery pack. On the right of the bay is a spring — unhook it from the silver case top. Some machines have one on the left as well.
6. Lever out the pin holding the silver case top to the graphite case bottom.
7. Unclip the silver case top from the graphite bottom with a small flat screwdriver, starting at the left edge where the pin came out. The right edge is held by a spike, so push the top towards the right to clear it.
8. Undo the screw holding the IrDA/power/battery connector board. The battery pack and circuit board now come out together.
9. Break the glue on the battery connector — it should give easily — and disconnect the pack.

The pack

Remove the plastic or tape encasing the cells and you will find:

• Two NiMH 700 mAh AAA cells
• A strip of circuit ribbon that the Revo uses as a temperature sensor — a thermistor

Start unwrapping from the left and take care not to break the thermistor. The charging circuit uses it to detect the thermal change that signals a full charge, so a damaged thermistor means a machine that never charges correctly.

Building the new pack

1. Desolder the connector from the old cells. Do not cut the wires — you need the connector and its full lead length.
2. Dispose of the old cells properly — not in household waste. See Battery Refurbishment for disposal guidance.
3. Solder the two new cells in series: the positive of one to the negative of the other.
4. Solder the connector on: red wire to positive, black to negative.
5. Re-encase the pack with heatshrink or tape, to hold the cells together and keep moisture out.
6. Hold the thermistor against the cell body as you wrap, exactly as it was.
7. Keep the pack as slender and as short as possible. There is very little room, and a bulky pack will not go back in.

Tape or heatshrink the pack just as securely as the original. Revos are known for batteries coming loose and unplugging — a problem Psion fixed in the Revo Plus.

Refitting

1. Plug the pack into the circuit board and put a small dab of glue over the connector to stop it working loose.
2. Use hot-melt glue or silicone sealer, not superglue — you may want to change the cells again, and hot-melt peels off with a little force once dry.
3. Refit the pack and circuit board. This is fiddly. Do not force anything — if a bulge is fouling, try rotating the pack.
4. Beware the microswitch on the rear. It turns the Revo on and off when the case is opened and closed, and it is easily broken by too much force when refitting the battery bay.
5. Push the case top back onto the screen and refit the pins. If the pack is not seated properly the Revo will have trouble opening or closing — check that before going further.
6. Glue the nameplate back with hot-melt, not superglue.

⚠️ The first charge — this part matters

Getting this wrong leaves you with a machine whose battery meter lies to you.

After replacing the cells:

1. Perform a hard reset.
2. Charge uninterrupted from 0 % to 100 % — about 6 hours for stock 700 mAh capacity — preferably with the unit switched off, so the hardware can recalibrate. This is the same procedure Psion specified for a new machine.
3. Ignore the battery meter during the first charge.
4. The red charging light turns off at around 84 % — that is normal and does not mean charging has finished.
5. If you fitted higher-capacity cells, work out how much longer the charge needs and extend it accordingly.

And one standing rule for the life of the machine:

Do not put either Revo model on charge when the battery is already above about 80 %. The charge termination depends on sensing a thermal change that occurs around that level; missing it can and does lead to overcharging.

Going further

The same teardown continues into the screen and mainboard, if you need to reach them:

• Pull out the screen hinge pins on either side of the keyboard to separate screen from keyboard — without twisting the ribbon cables.
• Prise up one corner of the keyboard and peel it off, then lever the PCB out from the front and flip it over. The speaker stays in the base.
• To free the screen ribbon, flip up the connector restraint and pull the ribbon out. With the restraint lifted the ribbon needs no force — if it resists, the restraint is not properly released. Do not force it.
• Prise the screen from its surround starting at the bottom, then up the sides. Too much pressure will shatter it.

This is genuinely risky. The documented attempt ended with a dented and scratched case and a broken case microswitch, costing the automatic open/close switching.

The backlight that isn't

There is a persistent story that the Revo's engineers left the wiring in place for a backlight and omitted only the lamps. Pads marked EL+ and EL− do exist under black tape on the screen PCB — but a voltmeter across them showed no reading, AC or DC, either with the unit on or with the Fn + Space sequence that activates the backlight on a Series 5.

Fitting a backlight to a Revo has not been shown to work. Treat it as an open question, not a project with a known answer.

Related pages

• Psion Revo · Psion Revo Plus
• Psion Revo General Maintenance · Psion Revo Troubleshooting Guide
• Battery Refurbishment — cell selection, soldering to tabs, testing and disposal
• Recommended Tools