Psion netBook Pro Battery Service

The main battery pack latches into the rear of the base. The two AAA backup cells live behind a cover above the keyboard on the left, reached by tilting the display slightly forward.

Battery service for the Psion netBook Pro.

The netBook Pro takes a higher-capacity pack than the EPOC machines and a completely different backup arrangement: two user-replaceable AAA alkaline cells in place of the CR2032. It also has something no earlier Psion had — a software fuel gauge that calibrates itself, and four specific events that throw that calibration away.

Psion Teklogix documented all of this in the user manual, which makes this the best-documented battery of any Psion covered on this wiki.

⚠️ Safety

Read Battery Refurbishment before opening any lithium pack. The netBook Pro's pack sits at up to 12.6 V fully charged and, like the earlier one, contains cells that are live at every stage of the work.

Always switch the machine off before removing the main battery.

If both the main pack and the backup cells go flat, everything in internal memory is lost. Only the flash folder survives — see below.

What the netBook Pro takes

Psion netBook Pro power

Item	Specification
Main battery	2200 mAh, 12.6 V Li-ion pack, 8 to 11 hours of operation depending on backlight level and with no peripheral cards
Backup battery	Two non-rechargeable alkaline AAA cells, user-replaceable
Charge time	3 to 4 hours. Constant-rate charging — no trickle charge and no fast charge
AC power	The manual specifies only "Adaptor for battery charging" and gives no electrical rating for it
Weight contribution	The machine weighs 1100 g including the 2200 mAh pack

Note the "12.6 V" figure is the full-charge voltage of a three-cell series pack — the same architecture as the netBook's, which Psion rated at 11.1 V nominal and 1500 mAh. A Usenet post from 2003 quotes a Psion brochure figure of "10.6 V 2200 mAh" for this pack; that does not match the manual or any other source and looks like a misreading of 12.6. Do not use 10.6 V.

Interchangeability with the classic netBook pack

A netBook Pro pack has been reported working in a classic netBook, and vice versa. In 2003 a netBook Pro tester "swapped the two batteries into the respective units and have used them for a week without any problem". The earlier community rebuild guide reaches the same conclusion from the other direction, observing that the Pro's pack "differs from that of the netBook only in the mAh rating of the batteries used for the pack".

Two caveats before you rely on that:

• It is a community report, not a manufacturer statement. One tester, one week, in 2003.
• The machines are close but not identical in size — 235 × 182 × 37 mm for the netBook against 235 × 184 × 35 mm for the Pro. Check the fit rather than forcing it.

The classic netBook's charger measures the real pack voltage and charges to 12.6 V regardless of capacity rating, so a higher-capacity pack simply takes longer to fill.

The fuel gauge, and how it loses calibration

This is the netBook Pro's distinctive behaviour and the source of most confusion about its battery.

The machine tracks discharge and charge current and voltage over a full cycle to build a picture of how that specific pack behaves. The Battery tab of Power Properties shows one of three states:

Battery gauge states

State	Meaning	Accuracy of the percentage
"Not calibrated"	The machine has not yet characterised this pack	Not very accurate
"Calibrating"	It is tracking a complete discharge and charge cycle	Somewhat more accurate
(no indicator)	Calibration complete	Should be very accurate

Once calibrated, the machine keeps refining its estimate on every full cycle, so the gauge adjusts itself for an ageing pack.

To calibrate a new or rebuilt pack

Psion Teklogix's own recommendation: fully charge the pack when first used, then fully discharge it before charging again.

A calibration cycle aborts if the AC power state changes — plugging in or unplugging the adapter mid-cycle — and charging calibration can also abort if the unit gets too hot.

The four events that reset it to "Not calibrated"

Calibration is lost, and the indicator reappears, if any of these occur:

1. The machine shuts off due to low battery while the capacity estimate still reads above 6 %.
2. Charging stops (charge current below 100 mA) while the estimate is below 94 %.
3. The estimate reaches 0 % and the machine keeps running for more than 15 minutes.
4. The estimate reaches 100 % and charging continues above 100 mA for more than 15 minutes.

Read that list as a diagnostic. Every one of those conditions is the gauge noticing that the pack no longer behaves as characterised — which, on a pack that has aged or been rebuilt with different cells, is exactly what you would expect. A netBook Pro that repeatedly returns to "Not calibrated" is telling you something true about its battery.

If you use more than one pack

There is a "Using multiple main battery packs" checkbox on the Battery tab. Ticked, the machine recalibrates each pack afresh every time one is inserted. Unticked, it keeps the calibration data when a pack is removed — which is right for a single pack and wrong for a rotation.

The Battery tab also shows live charge and discharge current, so you can watch consumption change as the backlight is adjusted or a card is inserted. The reading may be up to ten seconds old.

Changing the main pack

Psion Teklogix's procedure:

1. Switch the machine off.
2. Slide the battery pack latch towards the rear.
3. Pull the battery away from the machine.
4. Push in the replacement pack.

The backup cells hold the contents while you do this, and are "designed to maintain the memory for several hours".

One reassuring detail: when the machine shuts down on low battery, the pack still holds enough charge to preserve the system state without calling on the backup cells. Only if it is discharged further do the AAAs take over.

Changing the backup cells

The compartment is above the keyboard on the left, reached by tilting the display slightly forward.

1. Switch the machine off.
2. Angle the display slightly forward to expose the backup-battery cover.
3. Press down on the centre of the cover and slide it towards the front of the machine.
4. Remove the AAA cells.
5. Fit fresh alkaline AAA cells, observing the polarity marking.
6. Slide the cover back over the cells while again pressing down on its centre.

Use alkaline cells as specified. Leaked alkaline cells are one of the standard ways a machine like this is destroyed, so take them out if it is going into storage and check the compartment when it comes back — see Battery Explosion, Capacitor or Corrosion Damage.

For a hard reset, remove the backup cells before the main pack and refit them last, so they are not drained needlessly while the main pack is out.

Expected life, from the manufacturer

Unusually, Psion Teklogix published real ageing figures:

• Lithium-ion packs do not suddenly fail unless abused; capacity declines gradually.
• Capacity typically declines by 15–20 % of initial capacity over 400 charge/discharge cycles.
• Capacity also declines with age alone, in storage.
• End of life is conventionally 50 % of initial capacity, typically reached after approximately 1000 cycles — "although the battery will still work for some time after this point".

Applied to a machine now well over twenty years old, this says something blunt: every original netBook Pro pack is long past end of life on age alone, regardless of how few cycles it has seen.

Getting more runtime

Psion Teklogix's own list:

• Turn the screen brightness down.
• Set Switch to Suspend to 10 minutes in the Battery Power scheme.
• Work from internal storage rather than a memory card — writing to cards costs noticeably more power.
• Remove communications cards when not in use.

The three power-scheme timeouts — Switch to Dim, Switch to Stand-By and Switch to Suspend — are cumulative: the machine reaches Suspend only after all three have elapsed in turn. Psion Teklogix recommended a total of about 10 minutes. Waking from Dim and Stand-By is near-instantaneous, so a generous timeout costs nothing in responsiveness.

Protecting your data from a flat battery

Use the flash folder. About 10 MB of the machine's 32 MB of internal Flash is non-volatile storage whose contents survive a hard reset and the complete depletion of both the main and backup batteries.

A later ROM added Total Recall, a backup utility that can restore automatically after a hard reset. Its limitation is that individual files cannot be extracted from a backup set — it is all or nothing.

Rebuilding the pack

There is no netBook Pro-specific rebuild guide, but the pack is the same architecture as the classic netBook's — three 18650 cells in series with a protection and charge-control board — and the Psion netBook Battery Service procedure applies.

A collector re-celling one of these packs in 2023 recorded the sensible modern approach: use a spot welder rather than soldering to the cells. That is also this wiki's recommendation — see Battery Refurbishment for why, and for the cell-selection and welding technique.

Note that the Pro's pack was 2200 mAh from the factory, so a rebuild is a restoration rather than the substantial upgrade it is on a 1500 mAh netBook pack.

Buying, rather than building

Psionex in Lincoln lists an NB3000 main battery covering the netBook, netBook Pro and Series 7; it has been out of stock. The netBook Pro has no spare-parts category there at all beyond adapters, batteries, cases and docking.

AAA alkaline cells, of course, are available everywhere.

Related pages

• Psion netBook Pro · Psion netBook Pro General Maintenance · Psion netBook Pro Troubleshooting Guide
• Psion netBook Battery Service — the pack rebuild procedure
• Psion Series 7 Battery Service · Battery Refurbishment
• Battery Explosion, Capacitor or Corrosion Damage · Recommended Tools