charging the battery pack

I am looking for a charger to charge my plug in prius lifepo4 battery pack.
The pack has 70 cells in series, but i may increase that to 76 cells. I have just tested the PIS system, and electronically its working ok, but i am seeing a 10v sag on the batteries under load. The batteries currently at rest read 3.1v, they are not fully charged yet. I have the spare batteries here so its not a problem for me to increase the pack size, so as a test i may install an additional 6 batteries to see what effects that have during operation. I only intend to charge fully to 3.5v and hopefuly at rest this will equate to about 3.3v charged.

I havent got a charger yet, so i am open to suggestions on a budget.

I need a charger and I may have access to an old mes-dea charger that was fitted to a transit converted ev.
From the limited info I have found the charger is controlled by a pwm controller.

I do not have access to the controller, so will the charger work without the controller as a dumb charger, or is it useless without the controller, or can any charger controller work with the charger.
The charger is a 240v to 310 v dc charger and the profile for the charge curve is set in the pwm controller.

So, can I use it as a dumn charger, or is it useless without the pwm controller.

Or, if anyone has a charger they have no use for and want to sell it, let me know.

Many thanks for the advice. Anthony