To start, I’m sorry to hear that COVID-19 wrought such an enormous impact on you. As for an ebike, I think many in this community will agree that it’s quite the game changer, especially in lieu of a car and moreso in combination with public transport.

Your criteria to maximize range is perfectly reasonable in light of the restricted 24 kph – I’ll round to 25 to use more round numbers – regulations in your area. But is the 150 km (93 miles) figure intended to meet a specific use-case? That would be six hours in the saddle, which would give even very experienced acoustic road cyclists some substantial chafing in the bum area.

With that said, using one data point from a Class 1 ebike I purchased at auction and had a 500 Wh 48v battery pack, and limited to 32 kph (20 mph), it achieved a range of 37 miles (59 km) when run at full speed until near empty; the advertised range was 33 miles, so not bad at all. We’ll call it 50 km to keep things round, and to discount the human energy input.

Since energy consumption scales with velocity squared, reducing from 32 kph to your target 25 kph is a 1.6x speed reduction but should be a 2.56x energy reduction to run the same distance. Or alternatively, to run 2.56x farther on the same charge, which would be 128 km.

Supposing we discount that down to 100 km to be conservative, that would suggest 500 Wh can move for 100 km. This rate of 5 Wh/km is slightly more efficient than averaged statistics online, which cite an average of 8 Wh/km. But based on that, 750 Wh would achieve your 150 km target. The 48V 30Ah (1440 Wh) batteries you mentioned would be overachieving the target by a lot, even if your final build weight and efficiency was not as high as the auction ebike I compared to. One such 30Ah battery pack might weigh close to 8 kg – as I noted in my older comment about long range, speedy ebikes – so you wouldn’t want two of these unless you absolutely needed them.

That comment also discussed the issues with building your own battery packs, and in your case would have aesthetic implications: some transit operators may be reluctant to allow an ebike if it is “too DIY” or otherwise objectionable. A mass-production ebike would not tend to have this issue, usually being very stealth in regards to the electric capability.

On the flip side, designing and modifying an ebike is a fun hobby, and I’m slowly throwing my hat into that realm. But I think we need to take one step back and assess what’s prudent: are you looking for a DIY project, for a modern mode of transportation, or both?

A custom ebike will accomplish both, but as you said it’s a lot of effort, being an exercise in electronics and lithium ion battery packs, but also in bicycle maintenance. If you already have prior cycling experience, then there’s no reason you can’t learn everything you need to know from the Internet. On the flip side, I’ve settled on my personal opinion that having an ebike today is better than waiting for an ebike in two years: time will continue to make them more capable, cheaper, and more accessible, but that’s also time that you could be spent riding. So if you can meet your needs right now with a mass-production ebike, then I’m poised to say that you should just go for it and don’t look back. But reasonable minds will differ on that front.

Since 1 kWh is not terribly outlandish for some readily available ebikes, I would suggest you call round or visit some local bike shops that stock ebikes and ask for the ones with the most battery capacity. The ranges will often be based on a 32 kph pace, but if that advertised figure is over 100 km, then your desire for 150 km might already be met.