此類充電器構造簡單：一般由電源變壓器和四個二極管構成的橋式整流電路組成。充電的整個過程電壓保持不變，當電池的內阻隨著充電過程越來越小，因此充電電流也越來越大，產生的熱量也越來越多。電池快充飽時發熱量最大。加速電解質的分解，從而縮短了電池的壽命。早期的廠家生產的充電器采取“小心駛(shi)得萬年船”的策略，用(yong)小電(dian)(dian)流(liu)充(chong)(chong)電(dian)(dian)，一般不超過100mA ，這樣電(dian)(dian)池(chi)充(chong)(chong)到最后，發熱不至于(yu)太大(da)，從而延長(chang)電(dian)(dian)池(chi)壽(shou)命(ming)。缺點是充(chong)(chong)電(dian)(dian)時(shi)間長(chang)。現在生產這類(lei)的廠家，采用(yong)中(zhong)電(dian)(dian)流(liu)充(chong)(chong)電(dian)(dian)，100～200mA 充(chong)(chong)電(dian)(dian)時(shi)間大(da)大(da)縮短(duan)，但是以犧牲電(dian)(dian)池(chi)壽(shou)命(ming)為代價(jia)。傻瓜型充(chong)(chong)電(dian)(dian)器(qi)只能用(yong)時(shi)間來控制充(chong)(chong)電(dian)(dian)，它只適合于(yu)深充(chong)(chong)深放的五號、七號鎳(nie)鎘、鎳(nie)氫(qing)電(dian)(dian)池(chi)。

    充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時間(jian)：T = 1.5C/I（ C是(shi)電(dian)(dian)(dian)(dian)(dian)池容量，I是(shi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流）例：如果(guo)有個(ge)1000mAh 的(de)電(dian)(dian)(dian)(dian)(dian)池放在充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流是(shi)50mA的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)上充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時間(jian)就是(shi)30小(xiao)時。辨認這類充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)的(de)方(fang)法(fa)：當插上電(dian)(dian)(dian)(dian)(dian)源插頭后(hou)，充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)指示燈(deng)一直亮著。街上賣(mai)的(de)10～40元以(yi)內的(de)均是(shi)這種(zhong)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)。