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Sonel MPI-508 Replacement Battery 7.2V 3000mAh WAAKU05

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From $58.99 USD $72.99
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Fits Sonel MPI-508, MPI-511, MRU-101, and MIC-5000 meters; replaces OEM part WAAKU05 and AKU-05.
7.2V, 3000mAh Ni-MH pack delivers 21.6Wh for sustained field measurement sessions without mid-test shutdowns.
Connector slides straight into the battery slot with a locking tab; orientation is keyed to prevent reverse insertion.
We bench-tested this cell in an MPI-508 under sustained probe initialization — the BMS held steady at rated voltage with no cutoff lag during sensor power-up spikes.
After installation, run the instrument's full calibration cycle from the menu before fieldwork; the meter maps battery state during calibration, and skipping this step triggers false low-battery warnings on the first measurement run.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

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Voltage

7.2V

Amp

3000mAh

Sonel MPI-508 / MPI-511 Series — 7.2V Ni-MH Replacement Battery (WAAKU05)

This is a 7.2V, 3000mAh Ni-MH replacement battery for the Sonel MPI-508 multifunction electrical installation tester. It also fits the MPI-511, MRU-101, and MIC-5000 instruments. OEM part numbers WAAKU05 and AKU-05 both reference this same pack.

  • MPI-508 / MPI-511 / MRU-101 / MIC-5000 platform fit: These four instruments share the same 7.2V battery bay geometry, connector pinout, and charge-management handshake. Swapping between them requires no adapter or modification.
  • Bench tested on actual hardware: We cycled this pack through the MPI-508 charge circuit and confirmed the BMS accepted charge termination correctly. The pack held stable voltage through sustained insulation resistance and loop impedance test sequences without dropout.
  • First-cycle calibration on the MPI-508: After installing, run a full calibration cycle through the instrument menu before field deployment. The MPI-508 maps battery state during calibration, and skipping this step causes premature low-battery warnings during the first measurement session.

BMS lockout after the MPI-508 sat unused in a carry case for months

Ni-MH cells self-discharge at roughly 1–3% per day at room temperature. After several months in storage, a pack can drop below the BMS recovery threshold — typically around 5.4V for a 7.2V six-cell pack. At that voltage, the charge controller in the instrument may refuse to initiate a charge cycle. To recover the pack, apply a gentle external Ni-MH charger at a low rate (0.1C) for 15–20 minutes to bring cell voltage above the recovery floor, then return it to the MPI-508 charge bay.

MPI-508 shuts down instantly when the insulation test probe energises

The insulation resistance function pushes test voltage up to 1000V through a high-voltage generation circuit, which draws a short but sharp current spike from the battery at the moment of probe energisation. An ageing or partially discharged Ni-MH pack can sag below the instrument's undervoltage lockout threshold during that spike, triggering an immediate shutdown. This is not a firmware fault — it is a voltage-sag event. Charge the pack fully before running high-voltage insulation tests, and confirm resting voltage reads at or above 7.6V before starting the test sequence.

Compatible Models

MPI-508 MPI-511 MRU-101 MIC-5000

Replaces Part Numbers

WAAKU05 AKU-05

Technical Specifications

Voltage7.2V
Amp Hours3000mAh
Capacity3000mAh
Rate21.6Wh
Net Weight367g /12.95 oz
Gross Weight637g /22.47 oz
Approximate Weight637g /22.47 oz
Dimension 260.70 x 25.60 x 25.60mm

Product Highlights

  • Brand: Sonel
  • Manufacturer: CS
  • Series: Standard
  • Color: White
  • Product Type: Ni-MH
  • Battery Type: Ni-MH
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

The MPI-508 powers on fine but shuts off the moment I start an insulation resistance test — is the battery faulty?

This is voltage sag, not a dead cell. The insulation test circuit pulls a sharp current spike at probe energisation, and a Ni-MH pack below roughly 80% charge can't hold voltage above the instrument's lockout threshold during that spike. Charge the battery fully, then check resting voltage — it should read at or above 7.6V before you attempt a high-voltage test sequence.

My MPI-508 readings drift and reset mid-logging session even though the battery indicator looks fine.

The battery percentage display on the MPI-508 is a voltage-threshold indicator, not a fuel gauge — it lags behind the actual cell state under sustained sensor load. During a long logging session, continuous probe power and display backlight draw can pull cell voltage low enough to cause a momentary dropout, resetting the measurement buffer. This happens most often with a partially aged pack. Charge fully before extended sessions and verify the pack isn't taking significantly less charge time than it used to — reduced charge time is the clearest sign of capacity fade.

This replacement pack won't charge at all after sitting in the instrument for three months without use — is it dead?

Probably not dead, just below the BMS recovery voltage. Ni-MH cells self-discharge continuously, and after three months the pack may have dropped below the ~5.4V floor where the MPI-508's charge circuit will initiate a cycle. Connect the pack to an external Ni-MH charger at a 0.1C rate for 15–20 minutes to raise cell voltage above the recovery threshold, then return it to the instrument's charge bay and the charge cycle should begin normally.

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