Reading the code more, I think we might only need to change battery.c in board-specific directory instead of bd9995x driver.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/ec/+/d7a41825d936fd20c0dfafa0cc19d5fd66df575b

commit d7a41825d936fd20c0dfafa0cc19d5fd66df575b
Author: Caesar Wang <wxt@rock-chips.com>
Date: Thu Aug 17 03:46:37 2017

nefario/battery: support the 3s battery

As Nefario supports 3s battery, we can change the parameter
for board-specific instead of the charger driver.

BUG= chromium:754824 
BRANCH=none
TEST=Build and check battery information
> battery
  Status:    0x0080 INIT
  Param flags:00000003
  Temp:      0x0bc0 = 300.8 K (27.7 C)
  V:         0x2e1e = 11806 mV
  V-desired: 0x32fa = 13050 mV
  I:         0x07a7 = 1959 mA(CHG)
  I-desired: 0x0fa0 = 4000 mA
  Charging:  Allowed
  Charge:    17 %
  Manuf:     sunwoda
  Device:    BBLD485595
  Chem:      LION
  Serial:    0x0064
  V-design:  0x2c88 = 11400 mV
  Mode:      0x6001
  Abs charge:17 %
  Remaining: 667 mAh
  Cap-full:  4079 mAh
    Design:  4000 mAh
  Time-full: 2h:47

Change-Id: If9a4cdd9932e3287bf06cbe0840c94085cbeea1f
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/616508
Reviewed-by: Philip Chen <philipchen@chromium.org>
Reviewed-by: Shawn N <shawnn@chromium.org>

[modify] https://crrev.com/d7a41825d936fd20c0dfafa0cc19d5fd66df575b/board/nefario/battery.c

Correct, the bd9995x driver doesn't need to change. The driver contains the following function bd9995x_battery_charging_profile_settings(void) and that deals with all of the battery specific parameters which in turn are specified in the board battery.c file. There was an issue with the driver that was causing problems for fully discharged/no battery cases where a 3S + 1P battery was specified. But that's been addressed in this CL https://chromium-review.googlesource.com/c/602493