Just ordered a Bosch Lithium Iron Phosphate battery from EME
Not to be a downer on your choice of a new battery- but something didn’t seem quite correct to me for an older bike-A compatibility search yielded this-
Lithium Iron Phosphate (\(LiFePO_{4}\)) batteries are generally not recommended as a direct drop-in replacement for old BMW K75 motorcycles. While they offer significant weight savings, their charging requirements and cold-weather performance do not inherently match the design of classic K-bikes.
Understanding the constraints of the bike can help decide on the best setup:
The Problem Areas
- Charging System Voltage: The K75’s alternator and voltage regulator (especially the older 32A system) were designed for traditional lead-acid or AGM batteries. They typically regulate at roughly \(14.1\text{ V} – 14.4\text{ V}\), which can overcharge and permanently degrade a lithium battery over time.
Cold Weather Performance: Lithium batteries struggle significantly in cold weather. Their cranking amps drop drastically, meaning the bike may not start on a freezing day without “warming up” the battery first by running the headlight.
Parasitic Draw: Old K-bike wiring harnesses and clocks have a small, constant battery drain. \(LiFePO_{4}\) batteries have much less reserve capacity (Ah) than lead-acid ones and will go flat much faster if the bike sits idle.
Maintenance & Chargers: You cannot use a standard lead-acid trickle charger or desulfator on a lithium battery; you need a specific lithium-compatible charger.
What You Need to Make It Work
If you are determined to use a lithium battery for the weight savings or performance, you must modify the bike:
- Upgrade the Regulator: Replace the older stock regulator with a modern, solid-state unit (often a MOSFET style) to ensure the charging voltage doesn’t spike and overcook the battery.
Battery Management System (BMS): Only buy a powersports-specific lithium battery that features an internal BMS to protect against over-discharge, over-charge, and short circuits.
Disconnect During Storage: Install a battery tender disconnect, or completely isolate the battery if you plan to leave the motorcycle parked for more than a couple of weeks.
The Recommended Alternative
Most K75 purists and mechanics recommend sticking with a high-quality, sealed AGM battery (such as the Odyssey PC680). AGM batteries perfectly handle the stock charging system, are excellent at sitting idle without losing their charge, and provide reliable, massive cold-cranking amps (CCA).
Just thought I would throw it out there. Maybe you have taken all this into consideration. 
OM