Which battery on the TDM ?

The TDM900 is equipped with a GS - GT12B-4 battery. This is a Valve Regulated Lead-Acid (VRLA) battery with Active Glass Materiel (AGM) technology. It is maintenance-free & spill-free battery. It also have a lower self-discharge rate and is assumed to have a longer lifetime.

The TDM850 MkII 1996-2001 (4TX) is equipped with the same battery type.

The TDM850 MkI 1991-1995 (3VD) is equipped with a GS : GTX12-BS or Yuasa : YTX12B-BS classic lead-acid battery. This battery model is not suitable for the TDM850 (1996-2001) / TDM900 because of the casing size & positioning.
TDM900 & TDM850 (1996-2001)TDM850 (1991-1995)
Voltage12 V12V
Capacity10 AH10 AH
Recharging rate1.0 A x 10 hours1.0 A x 10 hours
Dimensions151 x 70 x 131 mm150 x 87 x 130 mm
Weight (approx.)4.5 kg / 10 lbs3.4 kg / 7.5 lbs

TDM900 / TDM850 MkII batteries test...

Battery reference is GT12B-4 (except Yuasa : YT12B-BS) under the JID standardization.
ManufacturerS-18°CS+18°CTimePriceEval.Q/P ratio
France Equipement3281h258922
OEM (brand)0301h218822
S-18°C : engine starts count @ -20°C.
S+18°C : engine starts count @ +18°C.
Time : slow discharge time count.
Price : Euros.

Source : Moto Magazine #212.
Prices may have changed since the test was released !
The Varta battery is not included in the test (ref : Funstart AGM 512 901 019 A514). This battery is quality equivalent to Yuasa.


• A Maintenance-Free (MF) batteries is sealed : no need to add water, no ventilation hose to inspect.
• A battery is prone to self-discharge even disconnected, especially in hot weather.
• A completely discharged battery permanently loses a significant part of its capacity.
• A battery is better preserved when fully charged and get a longer life.
• In case of prolonged immobilization, remove the battery, charge it completely and store in a cool, dry place. Recharge it periodically.
• Check the battery terminals: they oxidize and should be cleaned with a wire brush.


First of all, measure the voltage across the battery.
• 12.6 to 12.8 V100% charge
• 12.4 V 75% charge
• 12.1 V 50% charge
• 11.9 V 25% charge
• 11.8 V or less0% charge, replace battery.

Use a motorcycle battery charger with current limited to 1A max and observe the charging time.
After charging the voltage requires around one hour to stabilize before measuring.

Battery removal


• Remove the saddle.
• Disconnect the negative terminal.
• Disconnect the positive terminal.
• Remove the clamping rubber band.
• Rotate then pull-up from the plastic casing.

Replace in reverse order, use a flat screwdriver to help inserting the battery inside the plastic casing.
Some duct-tape will help for the next removal :



It's much more complicated - just like the Great Pyramid and its sarcophagus, the TDM850 was built around its battery !
There are several methods for the removal, more or less effective, but apparently this one is rather fast (get cake & tea ready) :

• Remove the bolts from rear brake cylinder and move it out the way.
• Remove the bolts securing the rear hugger allowing it to be pushed towards the back of the bike.
• Disconnect battery and remove bolts securing battery box.
• The battery can then be maneuvered around the rear shock and out past the brake cylinder.

It's a bit fiddly but shouldn't take any more than 5 mins.

Terms used for batteries

VLRA : Valve Regulated Lead Acid.
MF : Maintenance Free. The battery casing is sealed.
AGM : Absorbent Glass Mat. The acid of the battery is bonded to a non-woven glass fiber. Therefore the installation position does not matter.
GEL : Battery whose electrolyte is gelled with silica. An AGM battery is not a gel battery. This term is almost always used jointly and in advertisements for AGM batteries, but this is incorrect.

Links & documents

• GS Batteries main site
• Yuasa Batteries main site
• Understanding Motorcycle Batteries

• 2014 Yuasa Battery Specifications & Applications (PDF document 2.1 mb)
• 2014 Yuasa Technical Manual (PDF document 1.3 mb)

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