Shazaam's Tech Library - What replacement battery?

A useful technical article from guest contributor Larry Kelly of San Diego CA (aka Shazaam!).

916 specifc details , 996/998 specific details , more battery info

Think of your electrical system using a hydraulic analogy. Consider the battery is a six foot diameter one foot deep wading pool full of water. At the bottom of the pool is an three inch diameter drain pipe capped-off with a valve. Pumped water enters the top through a one inch diameter pipe.

Using this analogy,

Discharge current is the flow rate of water out of the pool
Charging current is the flow rate of water into the pool
Battery capacity is the volume of water in the pool.
Battery voltage is the water pressure at the bottom of the pool

Operating Condition: Storage

The drain valve is shut but the pool leaks a little (current). Every so often you put some more water in (trickle charging) the pool to make-up any water level (voltage). Over time the pool leaks more and more.

Operating Condition: Startup

Water flows (discharge current) rapidly out the open drain until simultaneously its valve is quickly shut and the pumped water (charging current) flows into the pool. During this time the pool has lost a gallon or two of water and the water level (voltage) drops a little.

Operating Condition: Normal Running

Water enters the pool faster than the water flows out the drain. After a while, the pool water level (voltage) rises and eventually overflows (fully charged battery).

OK, so what happens in this analogy if you use a smaller battery?

Instead of a six foot diameter one foot deep wading pool, suppose you have a three foot diameter one foot deep washtub.

Operating Condition: Storage

The washtub leaks at the same rate, so you put in some more water. Since the washtub is smaller the water level (voltage) drops faster so you have to full (trickle charge) it back up more often and for longer periods of time.

Operating Condition: Startup

Again, water flows rapidly out the open drain. But now the water level (voltage) has dropped much lower due to the smaller amount of water held by the washtub. The volume of water lost from the pool and the washtub is about the same.

Operating Condition: Normal Running

Again, water enters faster than the water drains, eventually overflowing the washtub, taking the same amount of time as before.

The principal advantage of using a larger battery is to be able to restart repeatedly. If you regularly don't ride long enough to recharge fully between restarts, stay with a larger capacity battery. Deep discharges will reduce battery life. A lower amp-hour battery will need to be trickle-charged more often.

916 Details

Standard battery 1994 - 2000 model years:

Yuasa YB16AL-A2 (16 AH, 200 CCA, 11.5 lbs.)

The principal advantage of using a larger battery is to be able to restart repeatedly and to deliver sufficient current to turn the starter motor. If you regularly don't ride long enough to recharge fully between restarts, stay with a larger capacity battery. A lower amp-hour battery will need to be trickle-charged more often. The chance of a deep discharge (that reduces battery life) is greater with smaller batteries. Further, the lower the temperature, the lower the current that can be supplied by any battery. Battery voltage is only an indicator of charge level, and has no relationship to a battery's ability to deliver an adequate starting current.

So early-916 batteries are rated at around 200 CCA, the current it can supply for 30 seconds at freezing temperatures. More at comfortable riding temps.

Consider also, that the early pre-1998 bikes have an alternator with a lower charging current output, so they'll take longer to fully recharge the battery. A prolonged 30 amp charging current is one contributing factor to why Ducati voltage regulator/rectifiers and stator wires fail prematurely.

I don’t know the exact specs on the Ducati starter motor, but in general, motorcycle-size starter motors draw around 30 amps under no load (max rpm) and around 85 amps under typical starting torque loads for unmodified motors. However, this figure can briefly rise to 300 amps under a stall condition typical of the initial start requirements of a high compression motor.

In 2001, all the superbikes were fited with a revised starter motor gear ratio that drew less current and made it possible to start the bike using a smaller battery. The starter gearing on the early bikes are not well suited to the smaller batteries.

996/998 Standard battery 2001 - 200X model years:

Yuasa YT12B-BS (10 AH, 125 CCA, 7.6 lbs.)

For the later bikes, and for track use of early bikes, the weight-saving battery-of-choice is the sealed and non-spillable AGM maintenance-free Yuasa YTZ7S. It's the same size as the later stock battery.

Yuasa YTZ7S (6 AH, 130 CCA, 4.6 lbs.)

So if you decide to replace a 916 battery that Ducati engineers say should deliver 200 amps with a battery that delivers 125 CCA, expect to stress your charging system and keep it on a trickle charger.

 

More battery info

The standard battery for the 1994 - 2000 model years, Yuasa YB16AL-A2 (16 AH, 200 CCA, 11.5 lbs., 8.125" x 2.8125" x 6.4375") is actually a very good choice. It's only drawback is that it requires attention to acid level.

Here are two maintenance free alternatives I've found that have better specs:

Fiamm-GS F19-12B (19 AH, 200 CCA, 7.13" x 3" x 6.6")
Odyssey PC680MJ (19 AH, 280 CCA, 14.7 lbs., 7.3" x 3.1" x 6.7") (dry cell technology, my personal choice)

The principal advantage of using a larger capacity battery is to be able to restart repeatedly. When you don't ride long enough to recharge fully between restarts, a larger capacity battery is an advantage. A lower capacity battery will need to be trickle-charged more often and the chance of a deep discharge (that reduces battery life) is greater with small capacity ones. Further, a battery's capacity drops when it gets cold so when you ride in cool weather, a smaller capacity battery will have an even smaller reserve for starting at low temperatures.

Consider also, that the early pre-1998 bikes have an alternator with a lower charging current output, so they'll take longer to fully recharge the battery. A prolonged 30 amp charging current is one contributing factor to why Ducati voltage regulator/rectifiers and stator wires fail prematurely.

In 2001, the bikes were fited with a revised starter motor gear ratio that drew less current and made it possible to start the bike using a smaller battery. The starter gearing on the early bikes are not well suited to the smaller batteries.

All non-stock aftermarket batteries will require some modifications to the hold-down system for installation. The most common problems are that it doesn't fit the stock battery tray, the terminal posts are switched negative to positive, (just turn it around) a wrong battery post connection type, and the stock retaining clip has nowhere on the battery casing to hook onto.

For example, I have an Odyssey PC680MJ battery installed in a 916. The installation requires rigging a custom hold-down strap and shimming the battery higher in the stock battery holder. Still, the larger width dimension will cause it to touch the inside of the fairing and distort it slightly. It is also heavier than the stock battery but he advantage is that it is higher capacity than stock and dry-cells don't discharge in storage as readily.

BTW, I installed the Odyssey PC680MJ in May 2001. It's still going strong.

 

Please note that Ducati-UpNorth.com cannot accept any liability for the accuracy or content of this section. Visitors who rely on this information do so at their own risk. If you are unsure it's worth contacting your local Ducati dealer who will be able to help. Do not attempt a repair or modification if you do not have the correct tools or knowledge to do so.