On battery doubt:
take out battery to get battery internal Resistance (BIR):
clip one of its terminal/pole the easier one, together with an end of R ~3-300 Ohm (depends on Vbat, Amp meter read quality) and one of the MM probe correctly by use of an alligator clip
the other R end is gathered with the other one of the MM probe correctly (+ red ,- black), touch it to the other battery end and read V on MM and write down!
subtract this V from the MM-read battery's V
divide the result by this V / R whatever R is, depends on Vbat, Amp meter quality to read the V/R
so:
(V batt. - V on R ) / (V on R / R)
if this BIR is greater ~ 0.5 - 0.7 Ohm it's time to replace
On PS check its V, I output, on I reading use highest then lowest I range in the order
if not as specification;
V, may some faulty in T or R get (semi) open
I, cap. bad high ESR usually the first and last cap.