Tuesday, Jul 04, 2017 at 09:50
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Absolutely agree with you Phil.
My pair of AGM's are charged each with its own 20 Amp dc-dc charger.
Both batteries are now 6 years old and going strong.
Previous AGM directly on the alternator and in the engine bay lasted 18 months.
Connecting directly to the alternator does not necessarily provide significantly faster full-charge times. It can depend on alternator output voltage which, with recent vehicles is decreasing.
With direct alternator charging, high currents may be achieved initially when the
battery is at a low state of charge but as the
battery voltage rises and the difference between alternator and
battery decreases, the charge current will progressively decrease. With a dc-dc multi-stage charger, the initial charge current is maintained throughout the 'bulk charge' phase so the contribution over a given period is improved.
If a person is determined to 'save money' by shunning dc-dc charging they would do better to also economise by purchasing a 'hybrid' auxiliary
battery which will accept a higher charge current. But they would then need to be careful regarding depth of discharge. There is no simple cheap way to get good performance from lead-acid
battery storage.
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