Psion netBook Battery Service

A netBook (right) beside an OLPC XO-1. Nothing about the netBook works without its pack: the internal disk is RAM, and the CR2032 backup cell holds it for hours, not weeks.

Battery service and pack rebuilding for the Psion netBook — and, because the pack is common to both, the Psion Series 7. The Windows CE machine takes a different pack and has its own page at Psion netBook Pro Battery Service.

This is the page that decides whether a netBook still works. No original pack survives in usable condition; Psion described the pack as sealed and non-serviceable; and the machine will not run from the mains adapter alone in any practical sense, because the internal disk is volatile RAM. Rebuilding the pack is therefore not an optional upgrade — it is the machine's continued existence.

⚠️ Safety

You are about to open a sealed lithium-ion pack and work on live cells. Read Battery Refurbishment first — it covers cell handling, thermal runaway, fire response and the tools in far more detail than this page repeats.

The specific hazards here:

• Three cells in series sit at up to 12.6 V fully charged, and every one of them is live the whole time. There is no discharged state in which this job is safe; a "flat" lithium cell still holds enough energy to weld metal.
• A shorted cell heats within seconds. One rebuilder's account is worth quoting in full because it describes exactly how these jobs go wrong: a solder spike on a cell tag pierced the plastic wrap of the adjacent cell and shorted onto the metal case beneath. "The tag got VERY HOT, VERY quickly. I burnt my fingers, but pulled the tag free before the cell exploded." The pack's controller was destroyed and the pack was never recognised by the machine again.
• Eye protection. The original guide is explicit about goggles.
• Work away from anything flammable, with a clear path to a door. A lithium cell in thermal runaway supplies its own oxidiser and cannot be smothered. See Battery Refurbishment for what to do and, more importantly, what not to attempt.
• Never bypass the controller board. See below.

The pack

Psion netBook and Series 7 battery pack

Item	Specification
Configuration	Three 18650 Li-ion cells in series (3S), plus a protection and charge-control board
Original cells	CGR18650H, 1500 mAh
Nominal voltage	11.1 V as Psion specified it. The Series 7 FAQ describes the same pack as "three 3.6v graphite-type Li-Ion cells", i.e. 10.8 V — the difference is the 3.6 V / 3.7 V nominal convention, not a different pack
Charge termination	12.6 V — 4.2 V per cell, measured by the machine, not assumed from a rating
Quoted runtime	8½ hours constant use; over 10 hours at minimum brightness with no peripherals
Charge time	Up to 3 hours, machine on or off
Backup cell	CR2032 lithium coin cell
External supply	15.5 V, 1.5 A, 100–240 V 50/60 Hz, with a ferrite core on the lead. RadioShack Adaptaplug "C": 4.75 mm OD, 1.75 mm ID, 1 cm long

Do not use another Psion adapter

The Series 7 and netBook are the odd ones out in the whole Psion range, and nothing else comes close to their supply requirement:

Psion mains adapter ratings

Machine	Voltage	Current
Series 7 / netBook	15.5 V	1.5 A
Series 5 / 5mx	6.0 V	1.0 A
Revo	6.0 V	500 mA
Series 3 / 3a / 3c / 3mx	9.0 V	250 mA
Siena	9.0 V	250 mA

One source gives the Series 7 adapter as 15 V rather than 15.5 V. The two disagree; both are enthusiast records rather than a Psion data sheet, and no manufacturer specification has survived to settle it.

Why the controller board matters

Never wire cells directly to the pack's external contacts.

The board inside the pack manages the charge and discharge of the cells individually. Without it, three cells in series will drift apart in state of charge, and eventually one is overcharged or driven below its safe floor while the pack as a whole looks fine.

The machine's charger is more sophisticated than it needs to be for its original cells, and this is what makes rebuilding worthwhile: it measures the real pack voltage and charges until it reaches 12.6 V. It is not set for 1500 mAh cells specifically. Higher-capacity cells simply take longer to reach the same termination voltage.

Rebuilding the pack

The community procedure below is the one published by OpenPsion, contributed by a rebuilder who did it on a Series 7 and reported 12½ hours of runtime with 2200 mAh cells, against 7 hours from the tired originals.

Read the whole procedure, and the soldering caution, before starting.

What you need

• Three 18650 Li-ion cells, matched. 2200 mAh or higher is the recommended and cost-effective choice; the originals were 1500 mAh.
• A multimeter.
• A spot welder and pure-nickel strip — see the caution below.
• Thin wire, good liquid flux, solder and a soldering iron, if you are following the original method.
• Thin screwdrivers and a thin knife.
• Glue or tape for reassembly.

1. Check the cells before you fit them

Confirm every new cell sits at the same voltage before connecting them in series. The original rebuilder measured 3.78 V on each. Cells at different states of charge will be forced into balance through whatever connects them, which at the currents involved is not a gentle process.

Buy cells you can trust. The 18650 market is full of relabelled and overstated cells; Battery Refurbishment covers how to tell.

2. Open the pack

The case is not designed to be opened, and you will break the internal locks getting in. Work the seam with thin screwdrivers and a thin knife. Plan to glue or tape it closed afterwards.

Inside are the three cells, welded together, and the white controller board.

3. Make the interconnects

Prepare four connection pieces before touching the cells, and keep them short. The two middle connections bridge cell to cell; the outer two go to the controller board.

4. ⚠️ Joining the cells — spot weld rather than solder

The published procedure solders directly to the cells. This wiki recommends spot welding instead, and you should understand why before choosing.

The original method is: sand a small patch of the terminal to give the solder something to key to, apply a drop of flux, and tin it in half a second, no more, cooling the cell immediately afterwards with a cotton pad soaked in alcohol. The author is explicit that overheating a Li-ion cell may damage it.

That works, and people have done it successfully. But it puts a soldering iron against a live lithium cell for a period judged by eye, and a cell's internals begin to degrade well below the temperature at which solder flows. A mini spot welder and pure-nickel strip delivers a 1–10 ms pulse that heats only the surface, and it is the method Battery Refurbishment recommends for exactly this reason. A collector re-celling a netBook Pro pack in 2023 reached the same conclusion independently: "Since there are 3 batteries in there, I'm going to try using a spot welder this time."

If you do solder anyway:

• Half a second on the cell, then cool it.
• Watch polarity on every joint.
• Keep the solder flat. File down any raised blob. This is not cosmetic — a solder spike is what pierced a neighbouring cell's wrap in the incident described above and nearly caused an explosion.
• Buy tagged cells if you can, to avoid soldering to the cell body at all.

5. Transfer the controller

Remove the old wires and old cells, and solder your new pack to the controller board. Keep the wires short.

6. Reassemble

Check for anything that could bear on a cell wrap before you close the case — a proud joint, a wire end, a burr. Insulate generously. Close the case with glue or tape, since the locks are gone.

7. First charge

Fit the pack and charge from the mains adapter. Remember that the charge LED goes out at about 70 % capacity, so let it run the full three hours rather than trusting the light.

Then run the machine down and watch what you get. A successful rebuild with 2200 mAh cells should comfortably beat the original 8½-hour figure.

Living with the pack

• There is no memory effect. Do not deep-cycle a lithium pack to "condition" it.
• Avoid running it flat. Li-ion cells last longest when they are not fully discharged.
• A spare pack wants a full charge every three months — and a full three hours, not until the LED goes out.
• Do not buy "new old stock" packs and store them. Lithium cells age from their manufacturing date, not from first use.
• Voltage across the terminals does not mean the pack is charged. It is not under load when you measure it.

The backup cell, and the trap

The CR2032 backup cell holds the RAM disk while the main pack is changed. It is a standard part and still trivially available.

But do not rely on it while removing the main pack. On some machines a microswitch in the battery catch turns the backlight on instead of shutting the machine down, and the resulting surge is more than the coin cell can carry — the entire internal disk is lost. The procedure for avoiding this is in the Series 7 troubleshooting guide and it is worth reading before you touch the catch.

Buying, rather than building

Psionex in Lincoln lists an NB3000 main battery for the netBook, netBook Pro and Series 7, and stocks the CR2032 backup cell. At the time of writing the main pack is out of stock and the coin cell is not.

That is the realistic position: the coin cell you can buy, the main pack you rebuild.

Related pages

• Psion netBook · Psion netBook General Maintenance · Psion netBook Troubleshooting Guide
• Psion Series 7 Battery Service · Psion netBook Pro Battery Service
• Battery Refurbishment — cell selection, spot welding, safety and fire response in detail
• Battery Explosion, Capacitor or Corrosion Damage · Recommended Tools