Hi Caps18, You have an interesting idea here,
From what i understand you thinking about having lithium and lead acid batteries in series running off the same charger at 156v. With an optional switch to just charge the lithium batteries at a 120v.
I am under the impression that lithium batteries (at least consumer batteries) require special charging methods compared to lead acid batteries
if your interested in knowing anything and everything about batteries this website has heaps of info about all battery types.
Charging lithium-ion batteries
The maximum current draw and supply of the battery bank will become the minimum of the lead acid or the lithium. So if the lead acid batteries can not supply much current the lead acid batteries will limit the current supply to the motor and the current charging rate. I havn't checked the max currents of lithium and lead acid batteries so not sure if its a problem but this might be something you want to look at.
Also running a charger and motor at 2 different voltages seems like a considerable amount of work
Regarding your 2nd comment about running only lithium batteries but at 2 different voltages. I like the idea of switching out discharged batteries. Some time ago i did a study for work on the concept that the better place was looking at. details can be found here for anyone interested
Better Place | The Global Provider of EV Networks and Services.
They are looking at having service station like locations which swap your whole battery bank for when you need to drive further than just say 100miles which the standard battery bank is capable of. Very cool idea and I think this idea has potential to make electric cars become more mainstream
So its all about decreasing the weight of the car which is why i like your idea of adding or removing batteries from your bank based on what distance you want to go. Unfortunately it is very difficult to do. If you swap in and out batteries in series the motor controller needs to be able to deal with the higher or lower input voltage which may compromise efficiency or abilities of the controller.
A better method would be to swap in another 120v rack of batteries which you connect in parallel. There may be issues in charging 2 paralleled battery packs, i think they will share current but i cant be sure without looking into it. Having 2 battery packs means you could connect up 1, when it discharges a switch / relay disconnects that battery pack and connects up the 2nd battery pack. So you can remove only the depleated pack.
Doing the same thing when the batteries are in series is increadibly difficult if not impossible. You can not make a set of given batteries discharge without the others discharging at the same level (there might be a way if you have electronic connection to each and every battery but thinking on the spot now i cant think of an way to do this)
Also regarding your comment at running at 156v pack at 120v is a good idea but in practice will significantly reduce the Ah of your pack when running at 120v. Batterys have a narrow band of voltage at which they can supply current, for example look at your standard consumer batteries you will get charge from them between say 2.2v and 1.8v. When you get below 1.8 v they have already lost almost all of their energy. So a 156v battery pack at 156v has 100% of its charge. The same battery pack at 120v may have only 20% of its charge.
Note also that some types of batteries will become perminately damaged if their charge drops below 20% which is why if you ever fully discharge your car battery a few times its never the same and you usually have to get a new one. Sorry i cant remember if lithium has the same characteristic.
Hope i havn't discouraged you, you have some great ideas here so i hope you find a way to achieve what you want. Look forward to seeing what you end up doing