Solar Charging - DC-DC Buck/Boost

My current home solar charging setup involves 2 100W solar panels in series fed to a MPT-7210A charge controller which charges a 2 kWh 14S 18650 pack (with BMS) during the day. My bike also uses 14S packs, but I use new high power cells on the bike, and salvaged laptop cells for the solar bank (so no battery swapping). When I pull into my garage after commuting, I charge my bike from a cycle satiator connected to the solar bank through a 120V AC inverter. I'd like to eliminate the inefficiency of intermediate DC-AC-DC conversion, but to charge from one battery to the other I believe I would need a 58.8V capable DC-DC buck/boost supply. This is because initially the voltage of the solar bank will be higher than the bike pack, but over the course of a charge, this will reverse.

Can anyone recommend a DC-DC buck/boost converter for this application? Low power (50-100W) is okay since I'll be charging overnight.

TIA

build your own based on a sepic converter ?

Just a word of caution, it really can be quite tricky to get a sepic working properly. An alternative is to use a boost converter but take the output from the output + and the input + terminals - you get a buck-boost then from a boost. It not very efficient and output voltage limit is now boost converter output voltage limit - input voltage.

https://www.fraron.de/en/a-85860059/

This is an interesting equation. The trouble with most cheap dc to dc step up converters is you can't go lower than the input voltage. Never heard of a sepic converter but could not find one on Ebay that would work. I had the same problem but was lucky to get over 100ah of free SLA batteries. I use this converter to charge my 15s, 26ah (up to 63v) from my SLAs



If you have access to your stay-at-home pack, and, own a solder iron, you could turn your 14s battery into 2, 7s packs. Then you could run the above converter bypassing your BMS and paralleling the 2, 7s connections. You could keep the same charging set-up and let your BMS balance the pack when you charge.