Mondeo / Sierra Battery

The differences in quoted voltages are due to the way the voltage is measured. Immediately after a start, battery voltage under full charge will rise to 14.2 volts, dropping to 13.8 as the battery reaches a fully charged state. These voltages are defined by the properties of the materials used, and are pretty much identical for all car batteries, even the one on my 40 year old Land Rover with a dynamo. Small voltage variations in use may be noted due to connection and cell internal resistances.

(For automotive lead acid batteries) * Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell) * Open-circuit at full discharge: 11.8 V to 12.0 V * Loaded at full discharge: 10.5 V. * Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells

1. All voltages are at 20 °C (68 °F), and must be adjusted

-0.022V/°C for temperature changes. 2. Float voltage recommendations vary, according to the manufacturer's recommendation. 3. Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) which is almost as detrimental as excessive voltage (causing corrosion and electrolyte loss)

• Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation) * Equalization charging (for flooded lead acids): 15 V for no more than 2 hours. Battery temperature must be monitored. * Gassing threshold: 14.4 V * After full charge, terminal voltage drops quickly to 13.2 V and then slowly to 12.6 V.

It's likely that a '99 Ford uses a silver calcium battery. You should not replace this with a standard lead-acid battery!

The silver calcium battery charges at a slightly higher voltage, which

If you car originally was fitted with a normal battery, it's acceptable to use the silver technology one; it might not quite reach absolute full charge, but in practice that won't be noticed.

The information will be in the owner's handbook.

Chris

Pretty well all car batteries are a nominal 12 volts - just like they always have been. The charging systems vary slightly - but in practice this can be ignored. Just check any battery you buy is listed as being correct for your model by the battery maker.

In general, I would agree with that, but using an older technology battery at the higher charging rate will shorten its life. Whether that's by a significant amount is debatable, but as the cost of the correct battery is not significantly higher (unless considering "bargain basement" ones, which I would avoid like the plague), then the OP would be best advised to get the correct one.

There is also evidence that obscure electrical faults on post-'99 Fords can be attributed to the use of the wrong battery type, in particular early Focus dashboard re-boots.

Chris

Thanks for all the advise. Just occured to me my old Sierra had L shape battery terminals, but the Mondeo has round post type. A Sierra battery with L shape terminals would not be suitable for my 99 Mondeo.